Eduard Monakhov

• Aßmann, Nicole; Hammann, Benjamin; Frøland, Mariann Carlsen; Kwapil, Wolfram & Monakhov, Eduard (2025). The differential impact of light soaking and dark annealing on hydrogen species during a LeTID cycle in boron-doped FZ silicon: A quantitative FT-IR study. Solar Energy Materials and Solar Cells. ISSN 0927-0248. 293. doi: 10.1016/j.solmat.2025.113853. Fulltekst i vitenarkiv Vis sammendrag

  Hydrogen is recognized as the key species responsible for light- and elevated- temperature-induced degradation (LeTID) in silicon. The simplest hydrogen species detectable is acceptor-hydrogen, HB in boron-doped material. Many studies track HB trough resistivity measurements and infer the evolution of the hydrogen molecule, H2, often excluding other potentially relevant hydrogen-related species from consideration. This study presents a Fourier transform-infrared analysis of the evolution of the hydrogen species, HB, H2, the hydrogen dimer , and the vacancy-hydrogen complexes VH4 and V2H6, during dark annealing and light soaking. The findings are compared to changes in lifetime-equivalent defect density observed over a LeTID cycle. Before solar cell processing the hydrogen species found are HB, H2, V2H6, and VH4. After processing, is formed, HB and H2 increase in concentration, while VH4 and V2H6 disappear. Light soaking at 75 °C and 1 sun-equivalent and dark annealing at 175 °C both reduce H2 and concentrations, while HB concentration increases with dark annealing but decreases during light soaking. Extended dark annealing results in a re-appearance of VH4. A considerable role of and VH4 in the hydrogen balance in a LeTID cycle is demonstrated. Finally, several unidentified peaks are observed in the wavenumber range of 3000cm−1 to 3300cm−1, showing sensitivity to different treatment conditions. Specifically, peaks at 3029.1cm−1, 3102.1cm−1, and 3238.9cm−1 grow only when light soaking took place as final step. Conversely, a peak at 3025.8cm−1 increases under dark annealing conditions and decreases with prolonged light soaking

• Azarov, Alexander; Radu, Cristian; Galeckas, Augustinas; Mercioniu, Ionel Florinel; Cernescu, Adrian & Venkatachalapathy, Vishnukanthan [Vis alle 11 forfattere av denne artikkelen] (2025). Self-Assembling of Multilayered Polymorphs with Ion Beams. Nano Letters. ISSN 1530-6984. 25(4), s. 1637–1643. doi: 10.1021/acs.nanolett.4c05727. Fulltekst i vitenarkiv
• Azarov, Alexander; Galeckas, Augustinas; Wendler, Elke; Monakhov, Eduard & Kuznetsov, Andrej (2024). Inverse dynamic defect annealing in ZnO. Applied Physics Letters. ISSN 0003-6951. 124(4). doi: 10.1063/5.0184669. Fulltekst i vitenarkiv Vis sammendrag

  Radiation tolerance of semiconductors depends on the dynamic defect annealing efficiency during irradiation. Consequently, it matters at what temperature one keeps the sample during irradiation, so that elevated temperatures typically result in lower remaining disorder. In the present work, we observed an opposite trend for the nitrogen ion implants into zinc oxide. Combining ion channeling technique, x-ray diffraction, and photoluminescence spectroscopy, we demonstrate that the interaction of nitrogen with radiation defects promotes an inverse dynamic annealing process, so that the increase in irradiation temperature leads to a more efficient defect formation. As a result, the residual radiation disorder is maximized at 650 °C and this state is characterized by the appearance of prominent optical signatures associated with zinc interstitials and strongly reduced strain accumulation as compared to the samples implanted at lower temperatures. However, for higher implantation temperatures, the impact of the inverse annealing decreases correlating with the surface degradation and loss of nitrogen.

• Azarov, Alexander; Galeckas, Augustinas; Cora, Ildikó; Fogarassy, Zsolt; Venkatachalapathy, Vishnukanthan & Monakhov, Eduard [Vis alle 7 forfattere av denne artikkelen] (2024). Optical Activity and Phase Transformations in γ/β Ga2O3 Bilayers Under Annealing. Advanced Optical Materials. doi: 10.1002/adom.202401325. Fulltekst i vitenarkiv Vis sammendrag

  Gallium oxide (Ga2O3) can be crystallized in several polymorphs exhibiting different physical properties. In this work, polymorphic structures consisting of the cubic defective spinel (γ) film on the top of the monoclinic (β) substrate are fabricated by disorder-induced ordering, known to be a practical way to stack these polymorphs together. Such bilayer structures are annealed to investigate optical properties and phase transformations. Specifically, photoluminescence and diffuse reflectance spectroscopy are combined with transmission electron microscopy, Rutherford backscattering/channeling spectrometry and X-ray diffraction to monitor the evolutions. As a result, a two-stage annealing kinetics is observed in γ/β Ga2O3 bilayers associated with the epitaxial γ-to-β regrowth at the interface at temperatures below 700 °C and a non-planar γ-to-β phase transformation starting at higher temperatures. Thus, the present data enhance understanding of the polymorphism in Ga2O3, interconnecting the phase transformation kinetics with the evolution of the optical properties.

• Aßmann, Nicole; Søndenå, Rune; Hammann, Benjamin; Kwapil, Wolfram & Monakhov, Eduard (2024). Reducing Time and Costs of FT-IR Studies of the Effect of SiNx, Dopants, and Emitter on Hydrogen Species in Si Wafers and Solar Cell Structures. SiliconPV Conference Proceedings. doi: 10.52825/siliconpv.v1i.840. Fulltekst i vitenarkiv Vis sammendrag

  Accurately measuring the hydrogen content in silicon (Si) solar cells is essential due to its connection to surface degradation and light and elevated temperature induced degradation (LeTID). Fourier Transform-Infrared (FT-IR) spectroscopy provides a quantitative technique for determining the content of various hydrogen species in Si wafers that have undergone various process steps. In this study, we examine both the effect of a silicon nitride (SiNx:H) layer during FT-IR spectroscopic measurements on hydrogen species, as well as the impact of an emitter present during firing on the amount of hydrogen introduced into Si wafers. We find that the presence of SiNx:H during measurements has negligible effects on the measured hydrogen species, potentially simplifying the preparation steps for FT-IR. For the emitter investigation we analyze boron (B)- and gallium (Ga)-doped p-type wafers to detect H-B, H-Ga, Oi-H2, and H2. We observe that hydrogen species initially present in B- and Ga-doped Si wafers differ significantly. Only H-Ga is detected in Ga-doped wafers, while H-B, Oi-H2, and H2 signals are measured in B-doped wafers. Moreover, we cannot confirm an increased release of H through the emitter into the bulk during the firing process. Finally, we conduct measurements at different temperatures and confirm that cryogenic temperatures are more effective for detecting H-B and H2 with concentrations in the 1014 cm-3 range. Nevertheless, useful spectra can still be obtained at liquid nitrogen (N2) temperatures.

• Rodrigues, Rodrigues Vieira; Hammann, B.; Aßmann, Nicole; Schön, J.; Kwapil, W. & Niewelt, T. [Vis alle 9 forfattere av denne artikkelen] (2024). Doping dependence of boron-hydrogen dynamics in crystalline silicon. Journal of Applied Physics. ISSN 0021-8979. 136(8). doi: 10.1063/5.0215089. Fulltekst i vitenarkiv Vis sammendrag

  In this contribution, we investigate the formation and dissociation of boron–hydrogen (BH) pairs in crystalline silicon under thermal equilibrium conditions. Our samples span doping concentrations of nearly two orders of magnitude and are passivated with a layer stack consisting of thin aluminum oxide and hydrogen-rich silicon nitride (Al 2O 3/SiN x:H). This layer stack acts as a hydrogen source during a following rapid thermal annealing. We characterize the samples using low-temperature Fourier-transform infrared spectroscopy and four-point-probe resistivity measurements. Our findings show that the proportion of hydrogen atoms initially bound to boron (BH pairs) rises with increasing boron concentration. Upon isothermal dark annealing at (163 ± 2) °C, hydrogen present in molecular form, H 2, dissociates at a rate directly proportional to the concentration of boron atoms, ∝ [ B −], leading to the formation of BH pairs. With prolonged annealing, an unknown hydrogen complex is formed at a rate that is inversely proportional to the square of the boron concentration, ∝ 1/[B − ] 2, resulting in the disappearance of BH pairs. Based on experimental observations, we derive a kinetic model in which we describe the formation of the unknown complex through neutral hydrogen H 0 binding to a sink. Additionally, we investigate the temperature dependence of the reaction rates and find that the H 2 dissociation process has an activation energy of (1.11 ± 0.05) eV, which is in close agreement with theoretical predictions.

• Azarov, Alexander; Galeckas, Augustinas; Mikhaylov, Alexey; Nikolskaya, Alena; Tetelbaum, David & Korolev, Dmitry [Vis alle 8 forfattere av denne artikkelen] (2024). Defect evolution and nitrogen incorporation in ion-implanted β-Ga2O3. Applied Physics Letters. ISSN 0003-6951. 125(19). doi: 10.1063/5.0239899. Fulltekst i vitenarkiv Vis sammendrag

  Nitrogen plays an important role in the Ga2O3-based device fabrication since it demonstrates a deep acceptor behavior and it can be used as a compensation impurity. In the present work, we introduced N into the monoclinic β-Ga2O3 single crystals by ion implantation using different dose-rates. The thermal evolution of the structural and optical properties of the implanted samples was studied by combining Rutherford backscattering/channeling spectrometry and x-ray diffraction with photoluminescence spectroscopy. We demonstrate that crystal disorder in N-implanted β-Ga2O3 is a strong function of ion flux even for room temperature implantation. Unlike other implanted species, the defect annealing kinetics for N exhibit a distinct two-stage behavior, where the low-temperature stage (<400 °C) is characterized by a rapid defect annealing, whereas the radiation defects exhibit a very slow evolution at the elevated temperatures (>400 °C). These trends are discussed in the framework of the disorder stabilization induced by the incorporation of the implanted N atoms into the Ga2O3 lattice. The obtained results can be used to better understand the interaction between N and intrinsic defects as well as to push forward the development of β-Ga2O3-based electronic devices.

• Søndenå, Rune; Weiser, Philip Michael; Mosel, Frank; Aßmann, Nicole; Hansen, Per-Anders Stensby & Monakhov, Eduard (2023). Controlling the hydrogen concentration in boron- and gallium-doped silicon wafers. AIP Conference Proceedings. ISSN 0094-243X. 2826(1), s. 110008-1–110008-6. doi: 10.1063/5.0141155. Fulltekst i vitenarkiv Vis sammendrag

  The influence of the thickness of the hydrogen-rich silicon nitride layer on the amount of hydrogen introduced into the bulk of silicon wafers, with boron or gallium as the acceptor dopant species, is investigated using cryogenic Fourier Transform-infrared spectroscopy. Nitride layers with comparable refractive indices are deposited on Czochralski wafers and subjected to a simulated contact firing process. Thus, hydrogenation of wafers is performed with different thicknesses of the respective hydrogen sources. Fourier Transform-infrared spectroscopy at 5.0 K show that the hydrogen concentrations can be varied by altering the film thickness. The effect of a subsequent passivation process, i.e. deposition of a second hydrogen rich dielectric film at an elevated temperature, is also investigated. We observe that the passivation may alter the states of hydrogen in the bulk silicon or cause unintentional introduction of hydrogen. This passivation process also revealed considerable differences between boron and gallium doped wafers; The hydrogen-boron concentration grew more than the corresponding hydrogen-gallium concentration during the passivation process.

• Povoli, Marco; Kok, Angela Chun Ying; Koybasi, Ozhan; Getz, Michael Norderhaug; O'Neill, George & Röhrich, Dieter [Vis alle 15 forfattere av denne artikkelen] (2023). 3D silicon detectors for neutron imaging applications. Journal of Instrumentation (JINST). 18, s. 1–12. doi: 10.1088/1748-0221/18/01/C01056. Fulltekst i vitenarkiv Vis sammendrag

  Neutron detection is of great importance in many fields spanning from scientific research, to nuclear science, and to medical application. The development of silicon-based neutron detectors with enhanced neutron detection efficiency can offer several advantages such as spatial resolution, enhanced dynamic range and background discrimination. In this work, increased detection efficiency is pursued by fabricating high aspect ratio 3D micro-structures filled with neutron converting materials (B4C) on planar silicon detectors. An in-depth feasibility study was carried out in all aspects of the sensor fabrication technology. Passivation of the etched structures was studied in detail, to ensure good electrical performance. The conformal deposition of B4C with a newly developed process showed excellent results. Preliminary electrical characterisation of the completed devices is promising, and detectors have been mounted on dedicated boards in view of the upcoming tests with neutrons.

• Saxegaard, Kjetil Karlsen; Monakhov, Eduard; Vines, Lasse & Bergum, Kristin (2023). Characteristics of ZnON films and heterojunction diodes with varying O:N ratios. Thin Solid Films. ISSN 0040-6090. 782. doi: 10.1016/j.tsf.2023.139968. Fulltekst i vitenarkiv Vis sammendrag

  Zinc Oxynitride (ZnOxNy) thin films display high mobilities and a considerable tunability of both the free electron concentration and optical band gap. The properties achievable for this material system makes ZnOxNy an intriguing n-type absorber candidate in silicon-based tandem solar cells. We have studied how the O:N ratio affect structural, optical and electrical properties of magnetron sputtered ZnOxNy thin films, as well the electrical behavior of ZnOxNy-Si pn heterojunction diodes. X-ray diffraction of the ZnOxNy films indicate either a Zn3N2-like structure or ZnO-like grains in combination with structural disorder. As the O:N ratio is increased, the optical band gap of ZnOxNy films increase from 1.1 to 1.9 eV. Hall effect measurements of the n-type ZnOxNy films show free electron concentrations varying with the O:N ratio, from 9.8 × 1017 to 1.5 × 1016 cm−3. Hall mobility up to 88 cm2∕Vs is achieved. We observe the formation of pn heterojunction diodes between ZnOxNy-films and p-Si. The electrical characteristics of these diodes are shown to depend on the ZnOxNy anion composition. Current rectification of 3.7 orders of magnitude is achieved between -1 and 1 V at room temperature. However, the built in voltage extracted from capacitance–voltage measurements are higher than theory suggest, implying an influence of defects on the electrical characteristics.

• Hammann, Benjamin; Assmann, Nicole; Weiser, Philip Michael; Kwapil, Wolfram; Niewelt, Tim & Schindler, Florian [Vis alle 9 forfattere av denne artikkelen] (2023). The Impact of Different Hydrogen Configurations on Light- and Elevated-Temperature- Induced Degradation. IEEE Journal of Photovoltaics. ISSN 2156-3381. 13(2), s. 224–235. doi: 10.1109/JPHOTOV.2023.3236185. Fulltekst i vitenarkiv Vis sammendrag

  In this article, the impact of different hydrogen configurations and their evolution on the extent and kinetics of light- and elevated-temperature-induced degradation (LeTID) is investigated in float-zone silicon via charge carrier lifetime measurements, low-temperature Fourier-transform infrared spectroscopy, and four-point-probe resistance measurements. Degradation conditions were light soaking at 77 °C and 1 sun-equivalent illumination intensity and dark anneal at 175 °C. The initial configuration of hydrogen is manipulated by varying the wafer thickness, the cooling ramp of the fast-firing process, and the dopant type (B- or P-doped). We find lower hydrogen concentrations in thinner samples and samples with a slower cooling ramp. This suggests that hydrogen diffuses out of the sample during the cool-down, which strongly affects the final concentration of hydrogen molecules H 2 , and to a smaller degree the concentration of boron-hydrogen (BH) pairs. A regeneration of potential LeTID defects and a presumed LeTID degradation during dark annealing is found in n-type Si. In p-type Si, the LeTID extent was found to scale with H 2 , suggesting a direct link between both. The temporal evolution of BH pairs, LeTID degradation/regeneration, and surface degradation depends on wafer thickness and the cooling ramp of the fast-firing process. Based upon these findings, we formulate a theory of the hydrogen-related mechanism behind LeTID: Hydrogen originating from H 2 moves between different temporary traps. First, hydrogen binds to LeTID precursors and acceptor atoms in the silicon bulk, later moving toward the surface. This leads first to the LeTID degradation and regeneration and then to the degradation of surface passivation.

• Hammann, Benjamin; Aßmann, Nicole; Schön, Jonas; Kwapil, Wolfram; Schindler, Florian & Roder, Sebastian [Vis alle 8 forfattere av denne artikkelen] (2023). Understanding the impact of the cooling ramp of the fast-firing process on light- and elevated-temperature-induced degradation. Solar Energy Materials and Solar Cells. ISSN 0927-0248. 259, s. 1–9. doi: 10.1016/j.solmat.2023.112462. Fulltekst i vitenarkiv
• Getz, Michael Norderhaug; Povoli, Marco; Koybasi, Ozhan; Slavicek, Tomas & Monakhov, Eduard (2023). Gamma-radiation hardness and long-term stability of ALD-Al2O3 surface passivated Si. Journal of Applied Physics. ISSN 0021-8979. 133(15). doi: 10.1063/5.0143013. Fulltekst i vitenarkiv Vis sammendrag

  Al2O3 has emerged as the surface passivation material of choice for p-type silicon in photovoltaics and has also become a candidate for passivating Si-based radiation sensors. However, the surface passivation of Al2O3 has been shown to degrade when exposed to gamma-radiation, making it of interest to determine methods of depositing Al2O3 that minimize the radiation-induced degradation on the surface passivation. In this study, we investigate the long-term stability and gamma-radiation hardness of Al2O3 prepared using the TMA+H2O+O3 precursor combination and how the pretreatment, the deposition temperature, and the film thickness affect the density of interface states, Dit, and fixed oxide charge, Qfix, before and after gamma-irradiation. We find that the surface saturation current density, J0s, of silicon passivated by Al2O3 increases after annealing but stabilizes over time depending on the Al2O3 thickness. Samples with thicknesses of &amp;lt;20 nm stabilize within hours, while those with &amp;gt;60 nm stabilize over days. J0s stabilizes at lower values with increased Al2O3 thickness. After exposure to 1 Mrad gamma-radiation, the samples still exhibit low Dit and high Qfix, with the best performing sample having a Dit of 1.5 × 1010 eV−1 cm−2 and a Qfix of −3.1 × 1012 cm−2. The deposition temperature appears to indirectly affect radiation hardness, owing to its impact on the hydrogen concentration in the film and at the Si–SiOx–Al2O3 interface. Lifetime measurements after irradiation indicate that Al2O3 still passivates the surface effectively. The carrier lifetime and Qfix can largely be recovered by annealing samples in O2 at 435 °C.

• Getz, Michael Norderhaug; Povoli, Marco & Monakhov, Eduard (2022). Improving ALD-Al2O3 Surface Passivation of Si Utilizing Pre-Existing SiOx. IEEE Journal of Photovoltaics. ISSN 2156-3381. 12(4), s. 929–936. doi: 10.1109/JPHOTOV.2022.3169985. Fulltekst i vitenarkiv Vis sammendrag

  Al 2 O 3 has rapidly become the surface passivation material of choice for p + layers of solar cells because of its high negative fixed charge, good long-term and thermal stability, and no parasitic absorption. In this article, the surface saturation current density, fixed charge, and interface state density are compared for Al 2 O 3 deposited on Si substrates where the pre-existing out-of-the-box SiO x layer was not removed, with substrates where the SiO x was removed by hydrofluoric acid. The depositions are performed by atomic layer deposition at temperatures in the 150–300 °C range, using trimethylaluminium, H 2 O, and O 3 as precursors. The samples where the native oxide was not removed achieve a higher level of surface passivation for every tested deposition temperature, with the sample deposited at 200 °C exhibiting a surface saturation current density of only 0.9 fA/cm 2 after annealing, a fixed charge of −4.2 × 10 12 cm −2 , and a density of interface states of 9.8 × 10 9 cm −2 eV −1 . Capacitance and conductance voltage characteristics reveal a strong correlation between the surface saturation current density and the density of interface states and fixed charges. It is also determined that the long-term stability of the surface passivation depends on the deposition temperature, with higher deposition temperatures resulting in improved long-term stability. The results indicate that H-terminated Si prior to Al 2 O 3 deposition may have a detrimental effect on the surface passivation.

• Søndenå, Rune; Weiser, Philip Michael & Monakhov, Eduard (2022). Direct and indirect determination of hydrogen-boron complexes in float-zone silicon wafers. I Brendel, Rolf; Ballif, Christophe; Dubois, Sebastien; Glunz, Stefan; Hahn, Giso; Poortmans, Jeff; Verlinden, Pierre & Weeber, Arthur (Red.), SiliconPV 2021, The 11th International Conference on Crystalline Silicon Photovoltaics. AIP Publishing (American Institute of Physics). ISSN 9780735443624. doi: 10.1063/5.0089274. Fulltekst i vitenarkiv
• Hammann, Benjamin; Aßmann, Nicole; Weiser, Philip Michael; Kwapil, Wolfram; Niewelt, Tim & Schindler, Florian [Vis alle 9 forfattere av denne artikkelen] (2022). Hydrogen complexes present after different firing profiles and their influence on LeTID degradation. Conference record of the Photovoltaic Specialists Conference. ISSN 0160-8371. doi: 10.1109/PVSC48317.2022.9938782. Fulltekst i vitenarkiv
• Thøgersen, Annett; Jensen, Ingvild Julie Thue; Belle, Branson Delano; Stange, Marit Synnøve Sæverud; Reinertsen, Vilde Mari & Kjeldstad, Torunn [Vis alle 9 forfattere av denne artikkelen] (2022). Plasmonic properties of aluminium nanowires in amorphous silicon. Journal of Physics: Condensed Matter. ISSN 0953-8984. 35(6), s. 1–10. doi: 10.1088/1361-648X/aca30e. Fulltekst i vitenarkiv Vis sammendrag

  Plasmonic structures can help enhance optical activity in the ultraviolet (UV) region and therefore enhancing photocatalytic reactions and the detection of organic and biological species. Most plasmonic structures are composed of Ag or Au. However, producing structures small enough for optical activity in the UV region has proved difficult. In this study, we demonstrate that aluminium nanowires are an excellent alternative. We investigated the plasmonic properties of the Al nanowires as well as the optoelectronic properties of the surrounding a − Si matrix by combining scanning transmission electron microscopy imaging, electron energy loss spectroscopy and electrodynamic modelling. We have found that the Al nanowires have distinct plasmonic modes in the UV and far UV region, from 0.75 eV to 13 eV. In addition, simulated results found that the size and spacing of the Al nanowires, as well as the embedding material were shown to have a large impact on the type of surface plasmon energies that can be generated in the material. Using electromagnetic modelling, we have identified the modes and illustrated how they could be tuned further.

• Azarov, Alexander; Bazioti, Kalliopi; Venkatachalapathy, Vishnukanthan; Ponniah, Vajeeston; Monakhov, Eduard & Kuznetsov, Andrej (2022). Disorder-Induced Ordering in Gallium Oxide Polymorphs. Physical Review Letters. ISSN 0031-9007. 128(1). doi: 10.1103/PhysRevLett.128.015704. Fulltekst i vitenarkiv Vis sammendrag

  olymorphs are common in nature and can be stabilized by applying external pressure in materials. The pressure and strain can also be induced by the gradually accumulated radiation disorder. However, in semiconductors, the radiation disorder accumulation typically results in the amorphization instead of engaging polymorphism. By studying these phenomena in gallium oxide we found that the amorphization may be prominently suppressed by the monoclinic to orthorhombic phase transition. Utilizing this discovery, a highly oriented single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated. Exploring this system, a novel mode of the lateral polymorphic regrowth, not previously observed in solids, was detected. In combination, these data envisage a new direction of research on polymorphs in Ga2O3 and, potentially, for similar polymorphic families in other materials.

• Fatima, K.; Song, Xin; Maryam, A.; Rasheed, M.N.; Iqbal, F. & Monakhov, Eduard [Vis alle 7 forfattere av denne artikkelen] (2021). Influence of environment on thermoelectric properties of n-type silicon-germanium alloy. Digest Journal of Nanomaterials and Biostructures. 16(3), s. 907–913. Fulltekst i vitenarkiv
• Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Vines, Lasse; Monakhov, Eduard; Lee, In-Hwan & Kuznetsov, Andrej (2021). Activation energy of silicon diffusion in gallium oxide: Roles of the mediating defects charge states and phase modification. Applied Physics Letters. ISSN 0003-6951. 119(18). doi: 10.1063/5.0070045. Fulltekst i vitenarkiv Vis sammendrag

  Silicon (Si) is an efficient n-type dopant in gallium oxide (Ga2O3)—an ultra-wide bandgap semiconductor promising in a number of applications. However, in spite of the technological importance for device fabrication, the activation energy for Si diffusion in Ga2O3 is missing in the literature. In the present work, we do such measurements in ion implanted monoclinic β-Ga2O3 samples employing anneals in air ambient, also admitting the influence of potential ion beam induced phase modifications on diffusion. Importantly, we show that Si diffusion in β-Ga2O3 fits with the concentration dependent diffusion model, involving neutral and single negatively charged point defects to mediate the process; so that we assumed gallium vacancies in the corresponding charge states to assist Si diffusion in β-Ga2O3 with activation energies of 3.2 ± 0.3 and 5.4 ± 0.4 eV, respectively. Moreover, we also found that a preexisting phase modified surface layer efficiently suppressed Si diffusion in β-Ga2O3 for temperatures up to 1000 °C.

• Nyborg, Martin; Azarov, Alexander; Bergum, Kristin & Monakhov, Eduard (2021). Deposition and characterization of lithium doped direct current magnetron sputtered Cu2O films. Thin Solid Films. ISSN 0040-6090. 722(31), s. 1–5. doi: 10.1016/j.tsf.2021.138573. Fulltekst i vitenarkiv
• Nyborg, Martin; Kolevatov, Ilia; Vasquez, Geraldo Cristian; Bergum, K. & Monakhov, E. (2021). Dominant defects and carrier transport in single crystalline cuprous oxide: A new attribution of optical transitions. Journal of Applied Physics. ISSN 0021-8979. 130(17). doi: 10.1063/5.0059406. Fulltekst i vitenarkiv Vis sammendrag

  Electronic properties of single crystal (111) Cu2O wafers have been investigated using a number of complementary techniques. Secondary ion mass spectrometry has shown significant presence of hydrogen and nitrogen. Cathodoluminescence measurements reveal strong near-band emission indicating the good electronic quality of the wafers. Two deep emission lines are observed at 1.3 and 1.7 eV. Temperature-dependent Hall effect measurements reveal electronic levels at around EV + 0.16 eV, EV + 0.22 eV, and ∼EV + 0.4 eV, where EV is the valence band edge. The discussion on the identity of the electronic centers calls for a revision of the traditional assignments of the 1.3-eV and 1.7-eV lines in order to take into account independent theoretical predictions. The temperature dependence of carrier mobility shows that the mechanism limiting the mobility can be described by scattering on neutral and ionized defect centers.

• Nyborg, Martin; Karlsen, Kjetil; Bergum, Kristin & Monakhov, Eduard (2021). Dominant acceptors in Li doped, magnetron deposited Cu2O films. Materials Research Express. 8(12), s. 1–8. doi: 10.1088/2053-1591/ac3e24. Fulltekst i vitenarkiv Vis sammendrag

  Cu 2 O films deposited by reactive magnetron sputtering with varying Li concentrations have been investigated by a combination of temperature-dependent Hall effect measurement and thermal admittance spectroscopy. As measured by secondary ion mass spectrometry, Li concentrations up to 5 × 10 20 Li/cm 3 have been achieved. Li doping significantly alters the electrical properties of Cu 2 O and increases hole concentration at room temperature for higher Li concentrations. Moreover, the apparent activation energy for the dominant acceptors decreases from around 0.2 eV for undoped or lightly doped Cu 2 O down to as low as 0.05 eV for higher Li concentrations.

• Zhu, Mengyi; Wu, Guixuan; Azarov, Alexander; Monakhov, Eduard; Tang, Kai & Müller, Michael [Vis alle 7 forfattere av denne artikkelen] (2021). Effects of La2O3 Addition into CaO-SiO2 Slag: Structural Evolution and Impurity Separation from Si-Sn Alloy. Metallurgical and Materials Transactions B. ISSN 1073-5615. 52B(5), s. 3045–3063. doi: 10.1007/s11663-021-02232-4. Fulltekst i vitenarkiv Vis sammendrag

  Boron (B) and phosphorus (P) are the most problematic impurities to be removed in the production of solar-grade silicon by the metallurgical process. In this work, the distribution of B and P between CaO-(La2O3)-SiO2 slags and Si-10 mass pct Sn melt was experimentally studied. B distribution coefficient increased from 2.93 in binary CaO-SiO2 slag to 3.33 and 3.65 with 2 and 10 mass pct La2O3 additions, respectively. In the followed acid-leaching experiments, the slag-treated Si-Sn alloys exhibited higher B and P removal than that of the initial alloy without slag treatment. Molecular dynamics simulations were performed to study the effect of La2O3 addition on the slag structural and transport properties. A novel oxygen classification method was proposed to distinguish the different structural roles of La and Ca in the CaO-La2O3-SiO2 system. It was found that La3+ prefers to stay in the depolymerized region, mostly connects with 6-7 non-bridging oxygen, and requires a weak charge compensation with Ca2+. Possible silicothermic reduction was evaluated to discuss the slag chemistry and the mass transfer between slag and metal phase. A thermodynamic model was derived to theoretically study the alloying effect on impurity distribution in slag refining where positive interaction coefficient and high alloying concentration were found most beneficial to improve the impurity removal.

• Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej (2021). Dominating migration barrier for intrinsic defects in gallium oxide: Dose-rate effect measurements. Applied Physics Letters. ISSN 0003-6951. 118(23). doi: 10.1063/5.0051047. Fulltekst i vitenarkiv Vis sammendrag

  Ion bombardment provides an opportunity to study basic properties of intrinsic defects in materials since the radiation-induced disorder accumulation depends on the balance between defect generation and migration rates. In particular, variation of such parameters as irradiation temperature and ion flux, known in the literature as dose-rate effect, interconnects the macroscopically measured lattice disorder with the migration barrier of the dominating defects. In this work, we measured the dose-rate effect in monoclinic gallium oxide (β-Ga2O3) and extracted its activation energy of 0.8 ± 0.1 eV in the range of 25–250 °C. Taking into account that the measurements were performed in the Ga-sublattice and considering 0.8 ± 0.1 eV in the context of theoretical data, we interpreted it as the migration barrier for Ga vacancies in β-Ga2O3, limiting the process. Additionally, we observed and took into account an interesting form of the lattice relaxation due to radiation-induced disorder buildup, interpreted in terms of the compressive strain accumulation, potentially trigging phase transitions in Ga2O3 lattice.

• Getz, Michael; Povoli, Marco & Monakhov, Eduard (2021). Effect of the native oxide on the Surface Passivation of Si by Al2O3. Journal of Applied Physics. ISSN 0021-8979. 129(20). doi: 10.1063/5.0051215. Fulltekst i vitenarkiv Vis sammendrag

  The effect of the native silicon oxide layer on the passivation properties of Al2O3 on p-type Si surfaces has been investigated. This was done by comparing effective carrier lifetime, surface saturation current density, fixed charge, and density of interface states of samples, where the native oxide was not removed prior to Al2O3 passivation, with samples subjected to a 3 min HF-dip. The sample with the native oxide exhibits excellent surface passivation post-annealing, with a surface saturation current density of 13 fA/cm2 and significantly longer effective lifetime compared to the sample, where the native oxide was removed. Capacitance–voltage measurements of a sample with the native oxide revealed a remarkably low density of interface states (1010 eV−1 cm−2), almost three times lower than a sample where the native oxide was removed prior to Al2O3 deposition. The results indicate that a thin layer of native oxide improves the Al2O3 surface passivation of silicon.

• Bonkerud, Julie; Zimmermann, Christian; Weiser, Philip Michael; Vines, Lasse & Monakhov, Eduard (2021). On the permittivity of titanium dioxide. Scientific Reports. 11. doi: 10.1038/s41598-021-92021-5. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Conductive rutile TiO 2 has received considerable attention recently due to multiple applications. However, the permittivity in conductive, reduced or doped TiO 2 appears to cause controversy with reported values in the range 100–10,000. In this work, we propose a method for measurements of the permittivity in conductive, n-type TiO 2 that involves: (i) hydrogen ion-implantation to form a donor concentration peak at a known depth, and (ii) capacitance–voltage measurements for donor profiling. We cannot confirm the claims stating an extremely high permittivity of single crystalline TiO 2 . On the contrary, the permittivity of conductive, reduced single crystalline TiO 2 is similar to that of insulating TiO 2 established previously, with a Curie–Weiss type temperature dependence and the values in the range 160–240 along with the c-axis.

• Fatima, Kaneez; Noor, Hadia; Ali, Adnan; Monakhov, Eduard & Asghar, Muhammad (2021). Annealing effect on seebeck coefficient of sige thin films deposited on quartz substrate. Coatings. 11(12). doi: 10.3390/coatings11121435. Fulltekst i vitenarkiv
• Assmann, Nicole; Persson, Clas; Kuznetsov, Andrej & Monakhov, Eduard (2021). Fine structure in electronic transitions attributed to nitrogen donor in silicon carbide. Applied Physics Letters. ISSN 0003-6951. 119(26). doi: 10.1063/5.0074046. Fulltekst i vitenarkiv Vis sammendrag

  Nitrogen in group-IV semiconductors has become a well-established element of qubits capable of room-temperature operation. In silicon carbide, nitrogen can occupy different nonequivalent lattice sites, giving rise to different shallow donor states. We report a triplet fine structure in electronic transitions of nitrogen donors on the quasi-cubic carbon site in 4H silicon carbide with activation enthalpies of around 100 meV. The intensities of triplet components have a prominent dependence on the voltage bias. The activation enthalpies of the transitions exhibit the Poole–Frenkel effect, while no bias dependence is observed for the magnitude of splitting. A tentative explanation of the fine structure involves local symmetry changes due to stacking faults.

• Bonkerud, Julie; Zimmermann, Christian; Weiser, Philip Michael; Aarholt, Thomas; Verhoeven, Espen Førdestrøm & Vines, Lasse [Vis alle 8 forfattere av denne artikkelen] (2020). Fabrication and characterization of Schottky barrier diodes on rutile TiO2. Materials Research Express. 7(6). doi: 10.1088/2053-1591/ab9777. Fulltekst i vitenarkiv
• Kjeldstad, Torunn; Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Jensen, Ingvild Julie Thue; Nilsen, Ola & Galeckas, Augustinas [Vis alle 7 forfattere av denne artikkelen] (2020). Selective etching of nanostructured a-Si:Al and its effect on porosity, Al gradient and surface oxidation. Thin Solid Films. ISSN 0040-6090. 702. doi: 10.1016/j.tsf.2020.137982. Fulltekst i vitenarkiv Vis sammendrag

  Nanoporous amorphous silicon (a-Si) with <5 nm cylindrical pores have been fabricated by phase separation of aluminum (Al) and silicon, forming self-assembled Al nanowires (NWs), followed by subsequent removal of Al by wet etching. This work studies the removal process of the Al NWs when using the different etchants HCl, H3PO4, and H2SO4. Total reflectance measurements are used in combination with theoretical modeling to estimate the lateral gradient of Al concentration formed during the etching process. X-ray Photoelectron Spectroscopy is used to show that the choice of Al etching agent has implications for the surface states of the remaining a-Si matrix. We have found that H3PO4 is the most efficient etching agent, while HCl provides a less oxidized a-Si matrix in addition to the least reflective surface. By varying the etching agent, the degree of surface oxidation and shape of Al gradient throughout the film can be tuned.

• Bonkerud, Julie; Zimmermann, Christian; Herklotz, Frank; Weiser, Philip Michael; Seiffert, Christoph & Verhoeven, Espen Førdestrøm [Vis alle 8 forfattere av denne artikkelen] (2020). Electrically-active defects in reduced and hydrogenated rutile TiO2. Semiconductor Science and Technology. ISSN 0268-1242. 36(1). doi: 10.1088/1361-6641/abc854. Fulltekst i vitenarkiv
• Weiser, Philip Michael; Zimmermann, Christian; Bonkerud, Julie; Vines, Lasse & Monakhov, Eduard (2020). Donors and polaronic absorption in rutile TiO2 single crystals. Journal of Applied Physics. ISSN 0021-8979. 128(14). doi: 10.1063/5.0027434. Fulltekst i vitenarkiv Vis sammendrag

  We have used a combination of optical absorption and electrical conductivity measurements to study the effect of the main donor on small polarons in rutile TiO2 single crystals rendered n-type conductive by hydrogenation or doping with Nb. The electrical conductivity measured at 295 K for hydrogenated samples shows a clear correlation with the interstitial hydrogen (Hi) concentration, which is consistent with reports that Hi is the main shallow donor in rutile TiO2. Conductive samples exhibit two distinct optical absorption bands in the IR spectral region, at ω1 = 6500 cm−1 (∼0.8 eV) and ω2 = 3100 cm−1 (∼0.4 eV), which are present in both hydrogen-rich and Nb-doped samples. The intensities of the absorption bands are proportional to the electrical conductivity, and they exhibit an Arrhenius-like temperature dependence for temperatures between 25–50 K and 50–100 K for H-doped and Nb-doped samples, respectively. The thermal activation energies (EAs) for the absorption bands depend strongly on the main donor: ω2 exhibits EA(H) and EA(Nb) of ∼4 and ∼10 meV, respectively, whereas ω1 shows EA(H) and EA(Nb) of ∼1 and ∼2 meV, respectively. The combination of temperature-dependent data for the optical absorption bands and interstitial deuterium (Di)-small polaron vibrational lines support a model where the thermal activation is associated with the reconfiguration of small polarons involving Ti sites far away from the donor. The thermal activation of the optical absorption bands gives us insight into the dynamics of donor-dependent small polaron reconfiguration in rutile TiO2.

• Ayedh, Hussein Mohammed Hussein; Monakhov, Eduard & Coutinho, J (2020). Formation and dissociation reactions of complexes involving interstitial carbon and oxygen defects in silicon. PHYSICAL REVIEW MATERIALS. 4(6). doi: 10.1103/PhysRevMaterials.4.064601. Fulltekst i vitenarkiv
• Zhu, Mengyi; Azarov, Alexander; Monakhov, Eduard; Tang, Kai & Safarian, Jafar (2020). Phosphorus separation from metallurgical-grade silicon by magnesium alloying and acid leaching. Separation and Purification Technology. ISSN 1383-5866. 240. doi: 10.1016/j.seppur.2020.116614. Fulltekst i vitenarkiv Vis sammendrag

  In this paper, the separation of phosphorus from metallurgical-grade silicon was investigated based on an Mg alloying and HCl leaching approach. Experimental results show that P concentration was reduced from initial 15.1 ppmw to 0.2 ppmw with also large extent removal of metallic impurities by two times Mg alloying-leaching purification. The mechanism of enhanced P separation is clarified owing to the strong affinity between Mg and P, which is validated by SIMS elemental mapping. A two-parameter analytical model was developed to predict the P removal degree based on the variables of alloying metal concentration and interaction coefficient between alloying metal and P. The model is validated with experimental results and the interaction coefficient ε^P_{Mg In Si} was obtained as −10.8. This approach can be applied to model the removal of impurity which follows Gulliver-Scheil solidification from other binary alloying systems. Furthermore, in order to study the effect of applied alloying-leaching operation times, a model was proposed which establishes the mathematical relationships among key processing variables like initial and target P concentrations, the amount of the alloying metal, and the process operation times.

• Azarov, Alexander; Galeckas, Augustinas; Venkatachalapathy, Vishnukanthan; Mei, Zengxia; Du, Xiaolong & Monakhov, Eduard [Vis alle 7 forfattere av denne artikkelen] (2020). Acceptor complex signatures in oxygen-rich ZnO thin films implanted with chlorine ions. Journal of Applied Physics. ISSN 0021-8979. 128. doi: 10.1063/5.0021089. Fulltekst i vitenarkiv Vis sammendrag

  Spectroscopic identification of defects and impurities is crucial for understanding doping asymmetry issues in ZnO and, therefore, realization of true ZnO-based bipolar devices. Chlorine (Cl) is an amphoteric impurity in ZnO exhibiting acceptor behavior in the interstitial configuration and donor action once on substitutional oxygen sites (ClO). In its turn, the incorporation of Cl atoms depends on the material growth conditions and a ClO fraction should be suppressed in O-rich materials. In the present work, Cl ions were implanted into ZnO thin films synthesized under O-rich conditions. In contrast to a negligible effect of Cl incorporation to electrical conductivity, photoluminescence measurements revealed dramatic developments of optical properties with a strong acceptor-like spectral signature emerging after 900 °C anneals. We discuss the origins of a new excitonic I* line (3.355 eV) induced by Cl-implantation and propose two alternative defect models based on shallow acceptor and shallow donor complexes.

• Gao, Xuejiao; Kolevatov, Ilia; Chen, Kaixiang; Guan, Bin; Mesli, Abdelmadjid & Monakhov, Eduard [Vis alle 7 forfattere av denne artikkelen] (2020). Full Activation of Boron in Silicon Doped by Self-Assembled Molecular Monolayers. ACS Applied Electronic Materials. 2(1), s. 268–274. doi: 10.1021/acsaelm.9b00748. Fulltekst i vitenarkiv Vis sammendrag

  Self-assembled molecular monolayer (SAMM) doping has great potential in state-of-the-art nanoelectronics with unique features of atomically precision and nondestructive doping on complex 3D surfaces. However, it was recently found that carbon impurities introduced by the SAMM significantly reduced the activation rate of phosphorus dopants by forming majority carrier traps. Developing a defect-free SAMM-doping technique with a high activation rate for dopants becomes critical for reliable applications. Considering that susbstitutional boron does not interact with carbon in silicon, herein we employ Hall measurements and secondary ion mass spectrometry (SIMS) to investigate the boron activation rate and then deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS) to analyze defects in boron-doped silicon by the SAMM technique. Unlike the phosphorus dopants, the activation rate of boron dopants is close to 100%, which is consistent with the defect measurement results (DLTS and MCTS). Only less than 1% boron dopants bind with oxygen impurities, forming majority hole traps. Interestingly, carbon-related defects in the form of CsH and CsOH act as minority trap states in boron-doped silicon, which will only capture electrons. As a result, the high concentration of carbon impurities has no impact on the activation rate of boron dopants.

• Gan, Jiantuo; Hoye, Robert L.Z; Levskaya, Yulia; Vines, Lasse; Marin, Andrew T. & MacManus-Driscoll, Judith L. [Vis alle 7 forfattere av denne artikkelen] (2020). Elucidating the origin of external quantum efficiency losses in cuprous oxide solar cells through defect analysis. Solar Energy Materials and Solar Cells. ISSN 0927-0248. 209. doi: 10.1016/j.solmat.2020.110418. Fulltekst i vitenarkiv Vis sammendrag

  Heterojunction Cu2O solar cells are an important class of Earth-abundant photovoltaics that can be synthesized by a variety of techniques, including electrochemical deposition (ECD) and thermal oxidation (TO). The latter gives the most efficient solar cells of up to 8.1% reported in the literature, but is limited by low external quantum efficiencies (EQE) in the long wavelength range (490–600 nm). By contrast, ECD Cu2O gives higher short wavelength EQEs of up to 90%. We elucidate the cause of this difference by characterizing and comparing ECD and TO films using impedance spectroscopy and fitting with a lumped circuit model to determine the trap density, followed by simulations. The data indicates that TO Cu2O has a higher density of interface defects, located approximately 0.5 eV above the valence band maximum (NV), and lower bulk defect density thus explaining the lower short wavelength EQEs and higher long wavelength EQEs. This work shows that a route to further efficiency increases of TO Cu2O is to reduce the density of interface defect states.

• Kumar, Raj; Bergum, Kristin; Riise, Heine Nygard; Monakhov, Eduard; Galeckas, Augustinas & Svensson, Bengt Gunnar (2020). Impact of post annealing and hydrogen implantation on functional properties of Cu2O thin films for photovoltaic applications. Journal of Alloys and Compounds. ISSN 0925-8388. 825(5), s. 1–8. doi: 10.1016/j.jallcom.2020.153982. Fulltekst i vitenarkiv Vis sammendrag

  Polycrystalline cuprous oxide (Cu2O) thin films were sputtered, annealed (900 °C rapid thermal annealing) and subsequently implanted with various hydrogen ion (H+) doses from 5E13 to 2E15 cm−2 with a low acceleration energy of 36 keV at room temperature to tailor the functional properties of the thin films for solar cell application. The annealed and H+ implanted Cu2O thin films were post annealed at low temperatures from 100 °C to 600 °C in an inert atmosphere to promote hydrogen passivation of prevalent intrinsic acceptors and tune the carrier concentration for optimum performance as an absorption layer in a heterojunction solar cell. The H+ incorporation and post annealing tuned the structural, optical and electrical properties of annealed polycrystalline Cu2O thin films. The results show an enhancement of the excitonic feature around ∼2.0 eV with H+ dose. The normalized photoluminescence (PL) area around ∼1.7 eV was drastically enhanced with increasing H+ doses compared to excitonic and copper vacancy related area. The normalized total PL quantum efficiency shows an enhancement in yield with elevated H+ doses by two orders of magnitude. The hole concentration decreases down to ∼1013 cm−3, while hole mobility and resistivity increase to ∼27 cm2/V and ∼2.4 kΩcm, respectively, as the H+ implantation goes from lower to higher doses. In addition, the post annealing and H+ incorporation lead to a change in the energy level of the major acceptor from 0.21 eV to 0.27 eV above the valence band maximum. By following the qualitative (PL analysis) and quantitative (Hall data) outcomes, we can conclude that H+ implantation and post annealing likely indicates the passivation of both acceptor defects and compensating donor defects.

• Weiser, Philip Michael; Monakhov, Eduard; Haug, Halvard; Wiig, Marie Syre & Søndenå, Rune (2020). Hydrogen-related defects measured by infrared spectroscopy in multicrystalline silicon wafers throughout an illuminated annealing process. Journal of Applied Physics. ISSN 0021-8979. 127(6). doi: 10.1063/1.5142476. Fulltekst i vitenarkiv Vis sammendrag

  Hydrogen (H) is thought to be strongly involved in the light and elevated temperature-induced degradation observed predominantly in p-type silicon wafers, but the nature of the defect or defects involved in this process is currently unknown. We have used infrared (IR) spectroscopy to detect the vibrational signatures due to the H–B, H–Ga, and H2*(C) defects in thin, hydrogenated, p-type multicrystalline silicon wafers after increasing the optical path length by preparation and polishing the edges of a stack of wafers. The concentrations of the H–B and H–Ga acceptor complexes are reduced to 80% of their starting values after low intensity (5 mW/cm2) illumination at room temperature for 96 h. Subsequent high intensity illumination (70 mW/cm2) at 150 °C for 7–8 h further decreases the concentrations of these defects; to ∼40% (H–B) and ∼50% (H–Ga) of their starting values. Our results show that, with careful sample preparation, IR spectroscopy can be used in conjunction with other techniques, e.g., quasisteady-state photoconductance, to investigate the involvement of different H-related point defects on degradation in solar-grade silicon wafers.

• Fara, Laurentiu; Chilibon, Irinela; Nordseth, Ørnulf; Craciunescu, Dan; Savastru, Dan & Vasiliu, Cristina [Vis alle 11 forfattere av denne artikkelen] (2020). Complex investigation of high efficiency and reliable heterojunction solar cell based on an improved Cu2O absorber layer. Energies. 13(18), s. 1–19. doi: 10.3390/en13184667. Fulltekst i vitenarkiv Vis sammendrag

  This study is aimed at increasing the performance and reliability of silicon-based heterojunction solar cells with advanced methods. This is achieved by a numerical electro-optical modeling and reliability analysis for such solar cells correlated with experimental analysis of the Cu2O absorber layer. It yields the optimization of a silicon tandem heterojunction solar cell based on a ZnO/Cu2O subcell and a c-Si bottom subcell using electro-optical numerical modeling. The buffer layer affinity and mobility together with a low conduction band offset for the heterojunction are discussed, as well as spectral properties of the device model. Experimental research of N-doped Cu2O thin films was dedicated to two main activities: (1) fabrication of specific samples by DC magnetron sputtering and (2) detailed characterization of the analyzed samples. This last investigation was based on advanced techniques: morphological (scanning electron microscopy—SEM and atomic force microscopy—AFM), structural (X-ray diffraction—XRD), and optical (spectroscopic ellipsometry—SE and Fourier-transform infrared spectroscopy—FTIR). This approach qualified the heterojunction solar cell based on cuprous oxide with nitrogen as an attractive candidate for high-performance solar devices. A reliability analysis based on Weibull statistical distribution establishes the degradation degree and failure rate of the studied solar cells under stress and under standard conditions.

• Kjeldstad, Torunn; Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Azarov, Alexander; Monakhov, Eduard & Galeckas, Augustinas (2019). Monitoring selective etching of self-assembled nanostructured a-Si:Al films. Nanotechnology. ISSN 0957-4484. 30(13), s. 1–5. doi: 10.1088/1361-6528/aafb86. Fulltekst i vitenarkiv Vis sammendrag

  Nanoporous and nanowire structures based on silicon (Si) have a well recognized potential in a number of applications such as photovoltaics, energy storage and thermoelectricity. The immiscibility of Si and aluminum (Al) may be utilized to produce a thin film of vertically aligned Al nanowires of 5 nm diameter within an amorphous silicon matrix (a-Si), providing a cheap and scalable fabrication method for sub 5 nm size Si nanostructures. In this work we study functionalization of these structures by removal of the Al nanowires. The nanowires have been etched by an aqueous solution of HCl, which results in a structure of vertically aligned nanochannels in a-Si with admixture of SiO x . The removal of Al nanowires has been monitored by several electron microscopy techniques, x-ray diffraction, Rutherford backscattering spectroscopy, and optical reflectance. We have established that optical reflectance measurements can reliably identify the complete removal of Al, confirmed by other techniques. This provides a robust and relatively simple method for controlling the nano-fabrication process on a macroscopic scale.

• Azarov, Alexander; Aarseth, Bjørn Lupton; Vines, Lasse; Hallen, Anders; Monakhov, Eduard & Kuznetsov, Andrej (2019). Defect annealing kinetics in ZnO implanted with Zn substituting elements: Zn interstitials and Li redistribution. Journal of Applied Physics. ISSN 0021-8979. 125(7). doi: 10.1063/1.5083226. Fulltekst i vitenarkiv Vis sammendrag

  It is known that the behavior of residual Li in ion implanted ZnO depends on the preferential localization of the implants, in particular, forming characteristic Li depleted or Li pile-up regions for Zn or O sublattice occupation of the implants due to the corresponding excess generation of Zn and O interstitials in accordance with the so-called “+1 model.” However, the present study reveals that conditions for the radiation damage annealing introduce additional complexity into the interpretation of the Li redistribution trends. Specifically, four implants residing predominantly in the Zn-sublattice, but exhibiting different lattice recovery routes, were considered. Analyzing Li redistribution trends in these samples, it is clearly shown that Li behavior depends on the defect annealing kinetics which is a strong function of the implanted fluence and ion species. Thus, Li depleted and Li pile-up regions (or even combinations of the two) were observed and correlated with the defect evolution in the samples. It is discussed how the observed Li redistribution trends can be used for better understanding a thermal evolution of point defects in ZnO and, in particular, energetics and migration properties of Zn interstitials.

• Nordseth, Ørnulf; Kumar, Raj; Bergum, Kristin; Chilibon, Irinela; Foss, Sean Erik & Monakhov, Eduard (2019). Nitrogen-Doped Cu2O Thin Films for Photovoltaic Applications. Materials. 12(18). doi: 10.3390/ma12183038. Fulltekst i vitenarkiv Vis sammendrag

  Cuprous oxide (Cu2O) is a p-type semiconductor with high optical absorption and a direct bandgap of about 2.1 eV, making it an attractive material for photovoltaic applications. For a high-performance photovoltaic device, the formation of low-resistivity contacts on Cu2O thin films is a prerequisite, which can be achieved by, for instance, nitrogen doping of Cu2O in order to increase the carrier concentration. In this work, nitrogen-doped p-type Cu2O thin films were prepared on quartz substrates by magnetron sputter deposition. By adding N2 gas during the deposition process, a nitrogen concentration of up to 2.3 × 1021 atoms/cm3 in the Cu2O thin films was achieved, as determined from secondary ion mass spectroscopy measurements. The effect of nitrogen doping on the structural, optical, and electrical properties of the Cu2O thin films was investigated. X-ray diffraction measurements suggest a preservation of the Cu2O phase for the nitrogen doped thin films, whereas spectrophotometric measurements show that the optical properties were not significantly altered by incorporation of nitrogen into the Cu2O matrix. A significant conductivity enhancement was achieved for the nitrogen-doped Cu2O thin films, based on Hall effect measurements, i.e., the hole concentration was increased from 4 × 1015 to 3 × 1019 cm−3 and the resistivity was reduced from 190 to 1.9 Ω⋅cm by adding nitrogen to the Cu2O thin films.

• Kjeldstad, Torunn; Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Jensen, Ingvild Julie Thue; Monakhov, Eduard & Galeckas, Augustinas (2019). Surface effects and optical properties of self-assembled nanostructured a-Si:Al. Nanomaterials. 9(8), s. 1–12. doi: 10.3390/nano9081106. Fulltekst i vitenarkiv Vis sammendrag

  We present a study of the surface effects and optical properties of the self-assembled nanostructures comprised of vertically aligned 5 nm-diameter Al nanowires embedded in an amorphous Si matrix (a-Si:Al). The controlled (partial) removal of Al nanowires in a selective etching process yielded nanoporous a-Si media with a variable effective surface area. Different spectroscopy techniques, such as X-ray photoelectron spectroscopy (XPS), UV-Vis spectrophotometry and photoluminescence (PL), have been combined to investigate the impact of such nanostructuring on optical absorption and emission properties. We also examine long-term exposure to air ambient and show that increasing level of surface oxidation determines the oxide defect-related nature of the dominant PL emission from the nanoporous structures. The role of bulk, nanosize and surface effects in optical properties has been separated and quantified, providing a better understanding of the potential of such nanoporous a-Si:Al structures for future device developments

• Ayedh, Hussein Mohammed Hussein; Grigorev, Aleksei; Galeckas, Augustinas; Svensson, Bengt Gunnar & Monakhov, Eduard (2019). Annealing Kinetics of the Interstitial Carbon–Dioxygen Complex in Silicon. Physica Status Solidi (a) applications and materials science. ISSN 1862-6300. 216(14), s. 1–5. doi: 10.1002/pssa.201800986. Fulltekst i vitenarkiv
• Kumar, Raj; Nordseth, Ørnulf; Vasquez, Geraldo Cristian; Foss, Sean Erik; Monakhov, Eduard & Svensson, Bengt Gunnar (2019). Investigation of n-Al:ZnO/p-Cu2O heterojunction for c-Si tandem heterojunction solar cell applications. AIP Conference Proceedings. ISSN 0094-243X. 2147(1). doi: 10.1063/1.5123885. Fulltekst i vitenarkiv Vis sammendrag

  In this work, an in-situ growth approach has been employed to fabricate Al:ZnO/Cu2O/Cu and Al:ZnO/ZnO/Cu2O/Cu heterojunctions using direct current (DC) and radio frequency (RF) magnetron sputtering technique in a controlled atmospheric condition. The effect of ZnO buffer layer thickness (30 and 50 nm) as well as in-situ Cu2O annealing at 600 °C in low vacuum (~ 10−6 Torr) prior to Al:ZnO deposition were studied. The carrier density of Al:ZnO was ~2 × 1020 cm3 with mobility ~8 cm2/V·s and resistivity ~1 × 10−3. Ω·cm, while the carrier density of Cu2O was 1 × 1015 cm3 with mobility ~19 cm2/V·s and resistivity ~200 .Ω·cm. The heterojunctions were investigated by depth resolved Cathodoluminescence (CL) spectroscopy at 80 K to analyze the influence of defects at the interface. The two emissions at 1.51 eV (Vo+) and 1.69 eV (Vo2+) dominate in all CL spectra related to oxygen vacancy defects in Cu2O. The relative intensity of the defect luminescence band Vo+ respect to Vo2+ is greater at the interface compared to bulk Cu2O, while the incorporation of the ZnO layer reduces significantly both radiative recombination and the Vo2+ related emission at the interface.

• Kolevatov, Ilia; Svensson, Bengt Gunnar & Monakhov, Eduard (2019). Correlated annealing and formation of vacancy-hydrogen related complexes in silicon. Journal of Physics: Condensed Matter. ISSN 0953-8984. 31(23), s. 1–5. doi: 10.1088/1361-648X/ab0bf2. Fulltekst i vitenarkiv Vis sammendrag

  We report on a deep level transient spectroscopy study of annealing kinetics of a deep, vacancy-hydrogen related level, labeled E5* , at 0.42 eV below the conduction band in hydrogen-implanted n-type silicon. The E5* annealing correlates with the formation of another commonly observed vacancy-hydrogen related level, labeled E5, at 0.45 eV below the conduction band. The annealing of E5* and the formation of E5 exhibit first-order kinetics with an activation energy of 1.61 ± 0.07 eV and a pre-factor of ~1013–1014 s−1 . The pre-factor indicates a dissociation or structural transformation mechanism. The analysis of electron capture cross-sections for E5* and E5 reveals considerable transition entropies for both states and a temperature dependent capture cross-section for E5* . Two possible identifications of E5* and E5 are put forward. Firstly, E5* can be attributed to V2H2(−/0) or V2H3(−/0), which dissociate with the emission of VH (E5). Secondly, E5* and E5 can be assigned to two different configurations of V3H.

• Azarov, Alexander; Wendler, Elke; Monakhov, Edouard & Svensson, Bengt Gunnar (2018). Defect stabilization and reverse annealing in ZnO implanted with nitrogen at room and cryogenic temperature. Journal of Applied Physics. ISSN 0021-8979. 123(10). doi: 10.1063/1.5022152. Fulltekst i vitenarkiv Vis sammendrag

  Despite the fact that nitrogen is a potential acceptor dopant and one of the most studied elements in ZnO, lacking understanding of associated defects and their thermal evolution limits realization of reliable p-type doping of ZnO. Here, we use ion implantation to introduce N at room temperature (RT) and 15 K in ZnO samples with/without a pre-existing buried disorder layer formed by Ag ion bombardment aligned along the [0001] direction. The buried layer contains a high concentration of extended defects, which act as traps for migrating point defects. Channeling analysis shows that reverse annealing occurs in all the N implanted samples during post-implant heat treatment above 600 °C with strong non-linear additive damage accumulation in the co-implanted samples. The reverse annealing effect is less stable in the RT co-implanted sample and the data suggest that a high local concentration of intrinsic point defects, like Zn interstitials, promotes the stability of the N-defect clusters responsible for the reverse annealing. This suggestion is also corroborated by enhanced and defect-mediated Ag outdiffusion at 1100 °C in the RT co-implanted samples.

• Zimmermann, Christian; Bonkerud, Julie; Herklotz, Frank; Sky, Thomas Neset; Hupfer, Alexander & Monakhov, Eduard [Vis alle 8 forfattere av denne artikkelen] (2018). Influence of annealing atmosphere on formation of electrically-active defects in rutile TiO2. Journal of Applied Physics. ISSN 0021-8979. 123(16), s. 161572-1–161572-8. doi: 10.1063/1.5011136. Fulltekst i vitenarkiv Vis sammendrag

  Electronic states in the upper part of the bandgap of reduced and/or hydrogenated n-type rutile TiO2 single crystals have been studied by means of thermal admittance and deep-level transient spectroscopy measurements. The studies were performed at sample temperatures between 28 and 300 K. The results reveal limited charge carrier freeze-out even at 28 K and evidence the existence of dominant shallow donors with ionization energies below 25 meV. Interstitial atomic hydrogen is considered to be a major contributor to these shallow donors, substantiated by infrared absorption measurements. Three defect energy levels with positions of about 70 meV, 95 meV, and 120 meV below the conduction band edge occur in all the studied samples, irrespective of the sample production batch and the post-growth heat treatment used. The origin of these levels is discussed in terms of electron polarons, intrinsic point defects, and/or common residual impurities, where especially interstitial titanium atoms, oxygen vacancies, and complexes involving Al atoms appear as likely candidates. In contrast, no common deep-level defect, exhibiting a charge state transition in the 200–700 meV range below the conduction band edge, is found in different samples. This may possibly indicate a strong influence on deep-level defects by the post-growth heat treatments employed.

• Kolevatov, Ilia; Weiser, Philip Michael; Monakhov, Eduard & Svensson, Bengt Gunnar (2018). Interaction Between Hydrogen and Vacancy Defects in Crystalline Silicon. Physica Status Solidi (a) applications and materials science. ISSN 1862-6300. s. 1–10. doi: 10.1002/pssa.201800670. Fulltekst i vitenarkiv
• Nordseth, Ørnulf; Kumar, Raj; Bergum, Kristin; Fara, Laurentiu; Dumitru, Constantin & Craciunescu, Dan [Vis alle 11 forfattere av denne artikkelen] (2018). Metal oxide thin-film heterojunctions for photovoltaic applications. Materials. 11(12), s. 1–10. doi: 10.3390/ma11122593. Fulltekst i vitenarkiv Vis sammendrag

  Silicon-based tandem solar cells incorporating low-cost, abundant, and non-toxic metal oxide materials can increase the conversion efficiency of silicon solar cells beyond their conventional limitations with obvious economic and environmental benefits. In this work, the electrical characteristics of a metal oxide thin-film heterojunction solar cell based on a cuprous oxide (Cu2O) absorber layer were investigated. Highly Al-doped n-type ZnO (AZO) and undoped p-type Cu2O thin films were prepared on quartz substrates by magnetron sputter deposition. The electrical and optical properties of these thin films were determined from Hall effect measurements and spectroscopic ellipsometry. After annealing the Cu2O film at 900 °C, the majority carrier (hole) mobility and the resistivity were measured at 50 cm2/V·s and 200 Ω·cm, respectively. Numerical modeling was carried out to investigate the effect of band alignment and interface defects on the electrical characteristics of the AZO/Cu2O heterojunction. The analysis suggests that the incorporation of a buffer layer can enhance the performance of the heterojunction solar cell as a result of reduced conduction band offset.

• Bergum, Kristin; Riise, Heine Nygard; Gorantla, Sandeep Madhukar; Lindberg, Per; Jensen, Ingvild Julie Thue & Gunnæs, Anette Eleonora [Vis alle 10 forfattere av denne artikkelen] (2018). Improving carrier transport in Cu2O thin films by rapid thermal annealing. Journal of Physics: Condensed Matter. ISSN 0953-8984. 30(7). doi: 10.1088/1361-648X/aaa5f4. Fulltekst i vitenarkiv
• Kolevatov, Ilia; Svensson, Bengt Gunnar & Monakhov, Eduard (2018). Interaction between the divacancy and hydrogen in silicon: Observation of fast and slow kinetics. Journal of Applied Physics. ISSN 0021-8979. 124(8). doi: 10.1063/1.5037310. Fulltekst i vitenarkiv Vis sammendrag

  The divacancy (V2) is one of the fundamental defects in silicon. However, the interaction of V2 with hydrogen is still not fully understood. In the present work, deep level transient spectroscopy (DLTS) results on hydrogen-assisted annealing of V2 are presented. H+ ions were implanted with multiple energies into n-type Czochralski-grown samples, yielding uniform (box-like) concentration-versus-depth profiles of V2 and hydrogen in the region probed by the DLTS measurements. The evolution kinetics of V2 reveals two distinct processes: (i) a fast one attributed to dissociation of phosphorus-hydrogen pairs and reaction with highly mobile atomic Hi and (ii) a slow one whose origin is not identified yet. During the slow process, we observe the formation of a hydrogen-related electronic state, labeled E5* and positioned ∼0.42 eV below the conduction band edge. The growth of E5* displays a close one-to-one proportionality with the loss of a V2-related DLTS peak, presumably due to V2H, overlapping with that of the single negatively charged V2.

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• Kjeldby, Snorre Braathen; Olsen, Vegard Skiftestad; Frodason, Ymir Kalmann; Zacharaki, Eirini; Cooil, Simon Phillip & Vines, Lasse [Vis alle 12 forfattere av denne artikkelen] (2025). Thin film top cell absorbers for multijunction solar cells. Fulltekst i vitenarkiv
• Azarov, Alexander & Monakhov, Eduard (2024). Hydrogen detection in Si by SIMS: Challenges and advantages. Fulltekst i vitenarkiv
• Azarov, Alexander; Galeckas, Augustinas; Cora, Ildikó; Fogarassy, Zsolt; Venkatachalapathy, Vishnukanthan & Monakhov, Eduard [Vis alle 7 forfattere av denne artikkelen] (2024). Thermal stability of double-layer gamma/beta Ga2O3 structures fabricated by ion beams. Fulltekst i vitenarkiv
• Aßmann, Nicole; Sondenå, Rune; Hammann, Benjamin; Kwapil, Wolfram & Monakhov, Eduard (2023). Reducing Time and Costs of FT-IR Studies of the Ef-fect of SiNx, Dopants, and Emitter on Hydrogen Spe-cies in Si Wafers and Solar Cell Structures. Fulltekst i vitenarkiv
• Kok, Angela Chun Ying; Choolakkal, Arun Haridas; Röhrich, Dieter; Monakhov, Eduard; O'Neill, George & Pedersen, Henrik [Vis alle 15 forfattere av denne artikkelen] (2023). INDet: Lessons Learnt from Boron-coated 3-D Silicon Detector Production. Fulltekst i vitenarkiv
• Azarov, Alexander; Park, Ji-Hyeon; Jeon, Dae-Woo; Monakhov, Eduard & Kuznetsov, Andrej (2023). Defect migration energies in Ga2O3 polymorphs measured by variations of temperature and flux under irradiation. Fulltekst i vitenarkiv
• Saxegaard, Kjetil Karlsen; Bergum, Kristin; Vines, Lasse & Monakhov, Eduard (2023). The effect of annealing on opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• Monakhov, Eduard; Bergum, Kristin; Vines, Lasse & Saxegaard, Kjetil Karlsen (2023). The UiO semiconductor group: Towards tandems with ZnON. Fulltekst i vitenarkiv
• Saxegaard, Kjetil Karlsen; Monakhov, Eduard; Vines, Lasse & Bergum, Kristin (2023). The effect of annealing on ZnON intended for solar cell applications. Fulltekst i vitenarkiv
• Saxegaard, Kjetil Karlsen; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• Azarov, Alexander; Bazioti, Kalliopi; Venkatachalapathy, Vishnukanthan; Vajeeston, Ponniah; Monakhov, Eduard & Kuznetsov, Andrej (2022). Disorder-induced ordering in Ga2O3 polymorphs. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnOxNy films. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). Electronic properties and dominant levels in ZnON. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnON films. Fulltekst i vitenarkiv
• O'Neill, George; Povoli, Marco; Kok, Angela Chun Ying; Koybasi, Ozhan; Getz, Michael Norderhaug & Röhrich, Dieter [Vis alle 15 forfattere av denne artikkelen] (2022). Predicting Efficiency of INDet Detectors. Fulltekst i vitenarkiv
• Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on Opto-electronic properties of ZnOxNy films. Fulltekst i vitenarkiv
• Povoli, Marco; Kok, Angela Chun Ying; Koybasi, Ozhan; Getz, Michael Norderhaug; Röhrich, Dieter & O'Neill, George [Vis alle 15 forfattere av denne artikkelen] (2022). 3D silicon detectors for neutron imaging applications. Fulltekst i vitenarkiv
• O'Neill, George; Povoli, Marco; Kok, Angela Chun Ying; Koybasi, Ozhan; Getz, Michael Norderhaug & Röhrich, Dieter [Vis alle 15 forfattere av denne artikkelen] (2022). Simulations Using NCrystal & Geant4 for Innovative Solid-state Neutron Detectors. Fulltekst i vitenarkiv
• Azarov, Alexander; Bazioti, Kalliopi; Venkatachalapathy, Vishnukanthan; Vajeeston, Ponniah; Monakhov, Eduard & Kuznetsov, Andrej (2022). Ion-beam-induced phase transitions in gallium oxide: impact of the implantation temperature. Fulltekst i vitenarkiv
• Bergum, Kristin; Monakhov, Eduard & Vines, Lasse (2022). The effect of oxygen and nitrogen concentrations on ZnON films. Fulltekst i vitenarkiv
• Vines, Lasse; Monakhov, Eduard & Kuznetsov, Andrej (2022). Defects in semiconductors. Journal of Applied Physics. ISSN 0021-8979. 132(15). doi: 10.1063/5.0127714. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Monakhov, Eduard; Vines, Lasse & Bergum, Kristin (2021). Electronic properties and the dominant levels in ZnON. Fulltekst i vitenarkiv
• Bergum, Kristin; Vines, Lasse & Monakhov, Eduard (2021). Electronic properties and the dominant levels in ZnON. Fulltekst i vitenarkiv
• Weiser, Philip Michael; Søndenå, Rune; Carcamo, Ruben; Farzad, Alireza & Monakhov, Eduard (2021). Characterization of hydrogen-related impurities in silicon and their connection to light induced degradation. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Monakhov, Eduard; Bergum, Kristin; Vines, Lasse & Jensen, Ingvild Thue (2021). Electronic properties and dominant levels in ZnON. Fulltekst i vitenarkiv
• Søndenå, Rune; Weiser, Philip Michael & Monakhov, Eduard (2021). Direct and Indirect Determination of Hydrogen-Boron Complexes in Float-Zone Silicon Wafers. Fulltekst i vitenarkiv
• Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej (2021). Dose-rate effect in β-Ga2O3. Fulltekst i vitenarkiv
• Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej (2021). Dominating migration barrier for intrinsic defects in gallium oxide at and above room temperature. Fulltekst i vitenarkiv
• Weiser, Philip Michael; Søndenå, Rune & Monakhov, Eduard (2021). Evolution of hydrogen-related defects in float zone-grown silicon wafers under dark annealing: resistivity change vs. FT-IR. Fulltekst i vitenarkiv
• Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej (2021). Radiation defect dynamics in β-Ga2O3: ion flux vs irradiation temperature. Fulltekst i vitenarkiv
• Azarov, Alexander; Hoseinpur, Arman; Safarian, Jafar & Monakhov, Eduard (2021). Impurity analysis in Al-Si alloys by SIMS: the role of the primary beam. Fulltekst i vitenarkiv
• Karlsen, Kjetil; Bergum, Kristin & Monakhov, Eduard (2020). ZnOxNy as a top cell absorber candidate in tandem solar cells. Fulltekst i vitenarkiv
• Kumar, Raj; Nordseth, Ørnulf; Foss, Sean Erik; Vasquez, Geraldo Cristian; Monakhov, Eduard & Svensson, Bengt Gunnar (2019). Investigation of n-Al:ZnO/p-Cu2O Heterojunction for c-Si Tandem Heterojunction Solar Cell Applications. Fulltekst i vitenarkiv
• Belle, Branson; Kutty, Maya N.; Koybasi, Ozhan; Dahl, Øystein; Azar, Amin S. & Taniguchi, Takashi [Vis alle 8 forfattere av denne artikkelen] (2018). Gamma ray radiation effects on h-BN encapsulated graphene field effect transistors. Fulltekst i vitenarkiv
• Nyborg, Martin; Bergum, Kristin; Monakhov, Eduard & Svensson, Bengt Gunnar (2018). Nitrogen Doping of Sputtered Cuprous Oxide Thin Films by ion Implantation. Fulltekst i vitenarkiv
• Nyborg, Martin; Monakhov, Eduard & Bergum, Kristin (2018). Lithium Doped DC Magnetron Sputtered Cu2O Thin Films. Fulltekst i vitenarkiv
• Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Galeckas, Augustinas; Nilsen, Ola & Monakhov, Eduard (2018). Aluminum nanowires in amorphous silicon. Fulltekst i vitenarkiv
• Kjeldstad, Torunn; Thøgersen, Annett; Galeckas, Augustinas; Monakhov, Eduard; Stange, Marit Synnøve Sæverud & Nilsen, Ola (2018). Aluminum nanowires in amorphous silicon. Fulltekst i vitenarkiv
• Panfilov, Daniil & Monakhov, Eduard (2023). Fabrication and characterisation of 4H-SiC diodes for particles detectors. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Silicon Carbide (SiC) radiation detectors are increasingly gaining recognition for their enhanced performance in diverse applications including nuclear radiation detection, functioning under high-temperature environments, x-ray detection, neutron detection and dosimetry. SiC comes out on top with its ability to operate efficiently in challenging environments. Compared to its primary competitor silicon (Si), 4H-SiC polytype has higher thermal conductivity, superior temperature stability, and a wider bandgap. In this thesis a scalable fabrication technique for n-type 4H-SiC Schottky diodes is proposed, serving as a stepping stone for the future fabrication of 4H-SiC-based detectors. The work encompasses the development and fine-tuning of photolithography processes, fabrication of 4H-SiC Schottky diodes, and their characterization. The photolithography process is based on the lift-off method. It involves two layers: (i) positive resist and (ii) a so-called lift-off layer to provide an undercut for easier removal of the resist. Such parameters as the exposure and development times were optimized. Optical microscopy and cross-sectional scanning electron microscopy were employed for optimizing the lithography process. Nickel, deposited by e-beam evaporation, was used for formation of Schottky diodes. Current-Voltage (IV) measurements show that the reverse-bias leakage current for most of the diodes is below the detection limit of the instruments used. The reverse saturation currents and the ideality factors are deduced from the fitting of the diode equation to the measurements for the forward bias. The lowest ideality factor and saturation current are 1.14 and 3.24∗10−21𝐴, respectively. The highest breakdown voltage obtained is 350 V. Capacitance-Voltage (CV) measurements have revealed the doping concentration in the epi-layer to be 1.2−1.3∗1016 𝑐𝑚−3. The depletion width at 100 V is deduced to be around 3 μm. The highest built-in voltage is found to be 1.6 V for 200 μm diodes, which is comparable with a theoretic value of 1.7 V. It is observed that smaller diodes (200 μm) demonstrate better characteristics, such as ideality factor, breakdown voltage and build-in voltage, compared to larger ones (2000 μm). We hypothesise that this is due to surface imperfections in the SiC epi-layer or dust particles from poor sample handling: As the diode size increases, there is a higher probability of a surface imperfection or a dust particle to occur between SiC and the metal, which will be detrimental for the Schottky diode. CV characterization of metal-oxide-semiconductor (MOS) structures is used to examine thermally grown silicon oxide (𝑆𝑖𝑂2) and aluminium oxide (𝐴𝑙2𝑂3), deposited by atomic layer deposition (ALD). MOS with thermally grown 𝑆𝑖𝑂2 reveal CV curves typical for a high-quality MOS structure, validating the insulating and passivating properties of the oxide. In comparison, ALD-grown 𝐴𝑙2 𝑂3 did not manifest reproducible and consistent CV characteristics.

• Ousdal, Erlend Lemva & Monakhov, Eduard (2020). Electrical and optical properties of graphene and graphene oxide: fundamentals and application. Universitetet i Oslo. Fulltekst i vitenarkiv
• Zariouh, Osama; Monakhov, Eduard & Bergum, Kristin (2020). Deposition of phase-pure Cu2O by magnetron sputtering. Universitetet i Oslo. Fulltekst i vitenarkiv
• Hall, Erlend; Monakhov, Eduard; Haug, Halvard & Marstein, Erik Stensrud (2020). Synthesis and characterisation of PEDOT:PSS/silicon interfaces for use in low cost, high efficiency solar cells. Universitetet i Oslo. Fulltekst i vitenarkiv
• Karlsen, Kjetil & Monakhov, Eduard (2019). Characterization of Li doped, magnetron sputtered Cu2O thin films. Universitetet i Oslo. Fulltekst i vitenarkiv
• Granerød, Cecilie Skjold; Prytz, Øystein; Monakhov, Eduard & Nilsen, Ola (2018). Measuring optical properties on the nanoscale: a STEM-EELS study of ZnO. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Denne avhandlingen bidrar til økt kunnskap om målinger av optiske egenskaper i halvledermaterialer gjennom å bruke en relativt ny og avansert målemetode. Denne målemetoden kan gi resultater med en ekstremt høy romlig oppløsning, og har derfor stort potensiale innen videre materialforskning. For å kunne videreutvikle dagens teknologi er det viktig å undersøke nye materialer og sammensetninger. Dette kan resultere i teknologi med høyere effektivitet, utvidede bruksområder, eller helt nye formål, som vil avhenge av materialets egenskaper. Båndgapet er en slik materialegenskap som betegner materialets konvertering mellom energi og strøm eller lys, og er derfor en viktig egenskap innen fornybar energi som solceller, eller i halvledermaterialer som brukes i elektronikk og LED-teknologi. De siste årene har det vært mulig å måle båndgap ved å benytte metoden elektron-energitapsspektroskopi (EELS) i et skanning-transmisjons-elektronmikroskop (STEM). Det unike ved denne metoden er en høy romlig oppløsning, som kan resultere i målinger med oppløsning på en nanometer-skala. Denne metoden kan dermed brukes til å studere båndgap og andre optiske egenskaper, og den romlige variasjonen av disse, og dermed bidra til ny informasjon om kvalitet, bruksområder og effektivitet i materialene. Båndgapsmålinger med denne metoden er ofte krevende å gjennomføre, men også å tolke. Dette arbeidet bidrar derfor med viktig forståelse for hvordan slike målinger og analyser kan gjennomføres, samt påpeke mulighetene og begrensningene ved metoden. Metoden har blitt testet på ulike systemer basert på sinkoksid (ZnO), som er et teknologisk viktig materiale for LED- og solcelleformål, og bidrar dermed også med nyttig informasjon om disse systemene.

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