GO-POW Defect control in Gallium Oxide for next gen POWer electronics

• Langørgen, Amanda; Frodason, Ymir Kalmann; Jensen, Ingvild Julie Thue; Turiansky, Mark E.; Walle, Chris G. Van de & Vines, Lasse (2025). Formation of the E4* level in implanted β-Ga2O3. PHYSICAL REVIEW MATERIALS. 9. doi: 10.1103/3ktr-6kmw. Fulltekst i vitenarkiv
• Kjeldby, Snorre Braathen; Nielsen, Dina Marie; Cooil, Simon Phillip; Frodason, Ymir Kalmann; Zacharaki, Eirini & Lee, In Hwan [Vis alle 10 forfattere av denne artikkelen] (2025). Tuning Properties of II-IV-Nitrides for Optoelectronic Applications. Advanced Optical Materials. 13(36). doi: 10.1002/adom.202502634. Fulltekst i vitenarkiv Vis sammendrag

  The earth-abundant II-IV-nitrides ZnSnN2 and ZnGeN2 are direct bandgap semiconductors with a wurtzite-derived crystal structure. Their alloys, ZnSnxGe1 − xN2, have bandgaps tunable across the full visible spectrum, making them interesting for many optoelectronic applications. Here, electrical, structural, and optical properties of near-stoichiometric ZnSnxGe1 − xN2 alloys, i.e., where [Zn]/([Zn]+[Ge]+[Sn]) ≈ 0.5, are reported, for samples synthesized by reactive magnetron sputtering. These results reveal unprecedentedly high electrical mobilities in Ge-rich alloys, with values of 136 and 400 cm2/Vs at room-temperature and ≈100 K, respectively. The bandgaps are determined from optical absorption measurements combined with hybrid density functional calculations and reveal a significant Burstein–Moss shift in the Sn rich alloys. Finally, band alignments are determined in the sputter-grown thin films by combining optical transmission measurements, hybrid density functional calculations, and UV photoelectron spectroscopy measurements, where the bandgap variation is predominantly caused by a shift of the conduction band edge. This work elucidates in unprecedented detail the tuning of optical and electrical properties in ZnSnxGe1 − xN2 by variation of the chemical composition, where bandgap values of alloys with x ∈ [0.5−0.7] are suitable for top cell absorbers in two-terminal tandem solar cells assuming a Si bottom cell.

• Arnab, K.A.; Stephens, M.; Maxfield, I.; Lee, C.; Ertekin, E. & Frodason, Ymir Kalmann [Vis alle 8 forfattere av denne artikkelen] (2025). Quantitative modeling of point defects in β-Ga2O3 combining hybrid functional energetics with semiconductor and processes thermodynamics. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 27, s. 11129–11143. doi: 10.1039/d4cp04817b. Fulltekst i vitenarkiv Vis sammendrag

  β-Gallium oxide (β-Ga2O3) is of high interest for power electronics because of its unique combination of melt growth, epitaxial growth, n-type dopability, ultrawide bandgap, and high critical field. Optimization of crystal growth processes to promote beneficial defects and suppress harmful ones requires accurate quantitative modelling of both native and impurity defects. Herein we quantitatively model defect concentrations as a function of bulk crystal growth conditions and demonstrate the necessity of including effects such as bandgap temperature dependence, chemical potentials from thermochemistry, and defect vibrational entropy in modelling based on defect formation energies computed by density functional theory (DFT) with hybrid functionals. Without these contributions, grossly-erroneous and misleading predictions arise, e.g. that n-type doping attempts would be fully compensated by Ga vacancies. Including these effects reproduces the experimental facts that melt-grown Sn-doped β-Ga2O3 crystals are conductive with small compensation while annealing the same crystals in O2 at intermediate temperatures renders them insulating. To accomplish this modeling, we developed a comprehensive modelling framework (KROGER) based on calculated defect formation energies and flexible thermodynamic conditions. These capabilities allow KROGER to capture full and partial defect equilibria amongst native defects and impurities occurring during specific semiconductor growth or fabrication processes. We use KROGER to model 873 charge-states of 259 defects involving 19 elements in conditions representing bulk crystal growth by edge-fed growth (EFG) and annealing in oxygen. Our methodology is transferrable to a wide range of materials beyond β-Ga2O3. The integration of thermodynamic and first-principles modelling of point defects provides insight into optimization of point defect populations in growth and processing.

• Hommedal, Ylva Knausgård; Bathen, Marianne Etzelmüller; Reinertsen, Vilde Mari; Johansen, Klaus Magnus H; Vines, Lasse & Frodason, Ymir Kalmann (2024). Theoretical modeling of defect diffusion in wide bandgap semiconductors. Journal of Applied Physics. ISSN 0021-8979. 135. doi: 10.1063/5.0205866. Fulltekst i vitenarkiv Vis sammendrag

  Since the 1940s, it has been known that diffusion in crystalline solids occurs due to lattice defects. The diffusion of defects can have a great impact on the processing and heat treatment of materials as the microstructural changes caused by diffusion can influence the material qualities and properties. It is, therefore, vital to be able to control the diffusion. This implies that we need a deep understanding of the interactions between impurities, matrix atoms, and intrinsic defects. The role of density functional theory (DFT) calculations in solid-state diffusion studies has become considerable. The main parameters to obtain in defect diffusion studies with DFT are formation energies, binding energies, and migration barriers. In particular, the utilization of the nudged elastic band and the dimer methods has improved the accuracy of these parameters. In systematic diffusion studies, the combination of experimentally obtained results and theoretical predictions can reveal information about the atomic diffusion processes. The combination of the theoretical predictions and the experimental results gives a unique opportunity to compare parameters found from the different methods and gain knowledge about atomic migration. In this Perspective paper, we present case studies on defect diffusion in wide bandgap semiconductors. The case studies cover examples from the three diffusion models: free diffusion, trap-limited diffusion, and reaction diffusion. We focus on the role of DFT in these studies combined with results obtained with the experimental techniques secondary ion mass spectrometry and deep-level transient spectroscopy combined with diffusion simulations.

• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Galeckas, Augustinas; Vines, Lasse & Johansen, Klaus Magnus H (2024). Broad luminescence from Zn acceptors in Zn doped β-Ga2O3. APL Materials. 12. doi: 10.1063/5.0190156. Fulltekst i vitenarkiv
• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2024). Diffusion of Ge Donors in β-Ga2O3. Physica status solidi (b). ISSN 0370-1972. doi: 10.1002/pssb.202400355. Fulltekst i vitenarkiv Vis sammendrag

  Diffusion of Ge donors in β-Ga2O3 is studied using a combination of secondary-ion mass spectrometry, diffusion simulations, and first-principles calculations, and compared to previous studies on Sn diffusion. Ge is implanted into (201)-oriented samples and annealed at temperatures from 900 to 1050 °C for a total of 8 h. From previous first-principles calculations, Sn is predicted to diffuse via the formation of a mobile complex with VGa that migrates through a sequence of exchange and rotation jumps. Herein, it is similarly predicted that Ge diffusion is mediated by VGa. However, the microscopic mechanism differs, as Ge can diffuse more easily through exchange combined with complex dissociation, rather than rotational jumps. This is explained by the difference in Ga-site preference of Ge compared to Sn, and the three-split mechanism that enables low migration barriers for VGa. The dissociation mechanism leads to a considerably faster transport for Ge as compared to Sn. The experimentally obtained Ge diffusion profiles are successfully fitted using a reaction–diffusion model based on the predicted diffusion mechanism, yielding a migration barrier of 2.5 ± 0.2 eV for the complex. The 2.72 eV obtained from first-principles calculations is in good agreement with this value.

• Gogova, D.; Tran, D.Q.; Stanishev, V.; Jokubavicius, V.; Vines, Lasse & Schubert, M. [Vis alle 9 forfattere av denne artikkelen] (2024). High crystalline quality homoepitaxial Si-doped β-Ga2O3(010) layers with reduced structural anisotropy grown by hot-wall MOCVD. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. ISSN 0734-2101. 42(2). doi: 10.1116/6.0003424. Fulltekst i vitenarkiv
• Langørgen, Amanda; Vines, Lasse & Frodason, Ymir Kalmann (2024). Perspective on electrically active defects in β- Ga2O3 from deep-level transient spectroscopy and first-principles calculations. Journal of Applied Physics. ISSN 0021-8979. 135(19). doi: 10.1063/5.0205950. Fulltekst i vitenarkiv Vis sammendrag

  The ultra-wide bandgap of gallium oxide provides a rich plethora of electrically active defects. Understanding and controlling such defects is of crucial importance in mature device processing. Deep-level transient spectroscopy is one of the most sensitive techniques for measuring electrically active defects in semiconductors and, hence, a key technique for progress toward gallium oxide-based components, including Schottky barrier diodes and field-effect transistors. However, deep-level transient spectroscopy does not provide chemical or configurational information about the defect signature and must, therefore, be combined with other experimental techniques or theoretical modeling to gain a deeper understanding of the defect physics. Here, we discuss the current status regarding the identification of electrically active defects in beta-phase gallium oxide, as observed by deep-level transient spectroscopy and supported by first-principles defect calculations based on the density functional theory. We also discuss the coordinated use of the experiment and theory as a powerful approach for studying electrically active defects and highlight some of the interesting but challenging issues related to the characterization and control of defects in this fascinating material.

• Frodason, Ymir Kalmann; Galeckas, Augustinas; Olsen, Vegard Skiftestad; Weiser, Philip Michael; Galazka, Zbigniew & Walle, Chris G. Van De [Vis alle 7 forfattere av denne artikkelen] (2024). Intrinsic origins of broad luminescence in melt-grown ZnGa2 O4 single crystals. PHYSICAL REVIEW MATERIALS. 8(9). doi: 10.1103/PhysRevMaterials.8.094604. Fulltekst i vitenarkiv
• Langørgen, Amanda; Frodason, Ymir Kalmann; Karsthof, Robert Michael; Wenckstern, Holger Von; Jensen, Ingvild Julie Thue & Vines, Lasse [Vis alle 7 forfattere av denne artikkelen] (2023). Defect level in κ-Ga2O3 revealed by thermal admittance spectroscopy. Journal of Applied Physics. ISSN 0021-8979. 134(1), s. 015701-1–015701-6. doi: 10.1063/5.0150994. Fulltekst i vitenarkiv Vis sammendrag

  Defects in pulsed-laser deposition grown have been investigated using thermal admittance spectroscopy and secondary ion mass spectrometry (SIMS). A film was grown on either a tin-doped indium oxide or an aluminum-doped zinc oxide buffer layer on a sapphire substrate functioning as back contact layer in vertical diode structures. In both sample types, a distinct signature in the capacitance signal was observed in the temperature range of 150–260 K. The corresponding defect charge-state transition level, labeled ⁠, was found to exhibit an activation energy of 0.21 eV. Potential candidates for the level were investigated using a combination of SIMS and hybrid-functional calculations. SIMS revealed the main impurities in the sample to be tin, silicon, and iron. The hybrid-functional calculations predict the acceptor levels of substitutional iron to lie 0.7–1.2 eV below the conduction band minimum depending on Ga-site, making an unlikely candidate for the level. Furthermore, Si as well as Sn substituting on the sixfold coordinated Ga2 site and the fivefold coordinated Ga3 and Ga4 sites are all shallow donors in -⁠, similar to that of -⁠. Sn substituting on the fourfold Ga1 site is, however, predicted to have levels in the bandgap at 0.15 and 0.24 eV below the conduction band minimum, in accordance with the extracted activation energy for ⁠. Thus, we tentatively assign as the origin of the level.

• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2023). Trap-limited diffusion of Zn in β-Ga2 O3. PHYSICAL REVIEW MATERIALS. 7(3), s. 1–8. doi: 10.1103/PhysRevMaterials.7.035401. Fulltekst i vitenarkiv Vis sammendrag

  Diffusion of Zn in (001)- and (¯201)-oriented β−Ga2O3 was studied using secondary-ion mass spectrometry and first-principles calculations based on hybrid and semilocal functionals. The β−Ga2O3 samples were sealed in quartz ampules together with a piece of metallic Zn and heated to temperatures of 900–1100 ∘C for 1 h. The Zn concentration profiles as a function of depth were simulated by employing the trap-limited diffusion model. From this model the migration barrier for Zn diffusion was found to be Em=2.2±0.2 and 2.1±0.1eV in the (001) and (¯201) orientations of β−Ga2O3, respectively, with corresponding dissociation energies of Ed = 3.5 ±1.1 and 3.2±0.6eV. Results from the first-principles calculations predict an interstitialcy mechanism for the Zn diffusion when it is not in its trapped state. Using the nudged elastic band method, we obtain a barrier of 1.6 eV for migration of Zn split interstitials (Zni) in both the [001] and [¯201] directions, in accordance with the results obtained from the trap-limited diffusion model. Interestingly, the Ga vacancy is found to be able to trap two Zn atoms forming a shallow donor complex labeled ZniZnGa. The energy needed for Zni to dissociate from this donor complex is estimated to be 2.99 eV, in reasonable agreement with the trap dissociation energies extracted from the diffusion model.

• Frodason, Ymir Kalmann; Varley, Joel B.; Johansen, Klaus Magnus H; Vines, Lasse & Walle, Chris G. Van De (2023). Migration of Ga vacancies and interstitials in β-Ga2 O3. Physical review B (PRB). ISSN 2469-9950. 107(2), s. 024109-1–024109-9. doi: 10.1103/PhysRevB.107.024109. Fulltekst i vitenarkiv Vis sammendrag

  Pathways and energy barriers for the migration of Ga vacancies (VGa) and Ga interstitials (Gai) in β−Ga2O3 are explored using hybrid functional calculations and the nudged elastic band method. Considering β−Ga2O3 as primarily being an n-type semiconductor, we focus on defect charge states relevant under such conditions: V3−Ga, Ga3+i, and Ga+i. Notably, we describe a mechanism by which VGa can transform between its different split configurations. In all cases, the intermediate state consists of a vacancy split between three Ga sites—a three-split vacancy—which enables passage over a significantly lower energy barrier. This is because it avoids the unfavorable simple vacancy at the tetrahedral Ga site. The proposed mechanism lowers the overall barrier for V3−Ga diffusion along the [001] crystal direction from 1.73 to 0.97 eV, whereas the 2.08 eV barrier for the [100] and [010] directions is unaffected. For Ga3+i, we obtain similar overall migration barriers of 0.72, 0.80, and 1.02 eV for the [010], [001], and [100] directions, respectively. Ga+i exhibits a strong preference for diffusion within the large eight-sided channel; the overall migration barrier is 0.92 eV for the [010] direction, and 2.16 eV for the [001] and [100] directions. The limiting step for the two latter directions involves ionization of Ga+i followed by a jump to an adjacent large eight-sided channel as Ga3+i. Our results are discussed in light of experimental observations of thermally activated recovery processes in irradiated material.

• Ghadi, Hemant; McGlone, Joe F.; Cornuelle, Evan; Senckowski, Alexander; Sharma, Shivam & Wong, Man Hoi [Vis alle 14 forfattere av denne artikkelen] (2023). Identification and characterization of deep nitrogen acceptors in beta-Ga2O3 using defect spectroscopies. APL Materials. 11(11). doi: 10.1063/5.0160541. Fulltekst i vitenarkiv Vis sammendrag

  The ability to achieve highly resistive beta-phase gallium oxide (β-Ga2O3) layers and substrates is critical for β-Ga2O3 high voltage and RF devices. To date, the most common approach involves doping with iron (Fe), which generates a moderately deep acceptor-like defect state located at EC-0.8 eV in the β-Ga2O3 bandgap. Recently, there has been growing interest in alternative acceptors, such as magnesium (Mg) and nitrogen (N), due to their predicted deeper energy levels, which could avoid inadvertent charge modulation during device operation. In this work, a systematic study that makes direct correlations between the introduction of N using ion implantation and the observation of a newly observed deep level at EC-2.9 eV detected by deep-level optical spectroscopy (DLOS) is presented. The concentration of this state displayed a monotonic dependence with N concentration over a range of implant conditions, as confirmed by secondary ion mass spectrometry (SIMS). With a near 1:1 match in absolute N and EC-2.9 eV trap concentrations from SIMS and DLOS, respectively, which also matched the measured removal of free electrons from capacitance-voltage studies, this indicates that N contributes a very efficiently incorporated compensating defect. Density functional theory calculations confirm the assignment of this state to be an N (0/−1) acceptor with a configuration of N occupying the oxygen site III [NO(III)]. The near ideal efficiency for this state to compensate free electrons and its location toward the midgap region of the β-Ga2O3 bandgap demonstrates the potential of N doping as a promising approach for producing semi-insulating β-Ga2O3.

• Ney, Verena; Henne, Bastian; Souza, Mariano de; Jantsch, Wolfgang; Johansen, Klaus Magnus Håland & Wilhelm, Fabrice [Vis alle 8 forfattere av denne artikkelen] (2023). Valence state, lattice incorporation, and resulting magnetic properties of Ni in Zn/Co-based magnetic oxides. Journal of Applied Physics. ISSN 0021-8979. 133(3). doi: 10.1063/5.0130731. Fulltekst i vitenarkiv Vis sammendrag

  Ni incorporation has been studied in a comprehensive range of Zn/Co-based magnetic oxides to elucidate its valence state and lattice incorporation. The resulting structural and magnetic properties of a range of related types of samples are studied in detail. On the one hand, Ni doping is studied in wurtzite ZnO which is either done by in-diffusion of the Ni into bulk ZnO or by reactive magnetron sputtering for Ni-doped thin films of ZnO. The latter is complemented by Ni and Co codoping of ZnO leading to altered magnetic properties which are then dominated by Co. On the other hand, the ZnCo2 O 4 spinel is codoped with varying amounts of Ni. In the wurtzite oxides, Ni is exclusively found on tetrahedral lattice sites in its formal 2+ oxidation state as deep donor. It behaves as an anisotropic paramagnet, and a limited solubility of Ni below 10% is found. Furthermore, the partial compensation of the antiferromagnetically coupled Co magnetic moments is induced by the Ni due to its smaller magnetic moment. In the ZnCo 2 O4 spinel, Ni is found to be incorporated in its formal 3+ oxidation state on octahedral sites and also couples antiferromagnetically to the Co moments. At low Ni concentrations, this leads to a lifting of the partial magnetic compensation of the antiferromagnetic ZnCo2 O 4 spinel and to ferrimagnetism at higher Ni concentrations. Increasing the Ni concentration even further leads to phase separation of cubic NiO resulting in a structurally less defined, exchange-biased composite magnetic oxide.

• Borgersen, Jon; Karsthof, Robert Michael; Rønning, Vegard; Vines, Lasse; Wenckstern, Holger Von & Grundmann, Marius [Vis alle 8 forfattere av denne artikkelen] (2023). Origin of enhanced conductivity in low dose ion irradiated oxides. AIP Advances. 13(1), s. 015211-1–015211-5. doi: 10.1063/5.0134699. Fulltekst i vitenarkiv Vis sammendrag

  Significant resistivity variations have previously been observed in oxides subjected to relatively low ion irradiation doses, nominally insufficient to generate the amount of bulk defects needed to explain the phenomena. In an effort to unveil the underlying mechanisms, we performed a systematic comparative study of the resistivity evolution in In 2 O 3 -based oxides as a function of low ion doses and ultraviolet (UV) illumination, observing striking correlations. Specifically, we found that irradiation with ∼3 × 10 12  Si/cm 2 and ∼18 h UV exposure result in similar resistivity drops, interpreted in terms of irradiation/illumination assisted desorption of oxygen containing species from the surface. This was further proven by post-irradiation exposure of one of the samples to an oxygen atmosphere partially restoring the resistivity. Combining the present results with literature data, we conclude that the radiation tolerance of In 2 O 3 -based and similar oxides depends on the surface charge modifications, individual defect contributions, and contributions from defect complexes at low, intermediate, and high doses, respectively.

• Frodason, Ymir Kalmann; Krzyzaniak, Patryk Piotr; Vines, Lasse; Varley, Joel Basile; Walle, Chris G. Van De & Johansen, Klaus Magnus H (2023). Diffusion of Sn donors in β-Ga2O3. APL Materials. 11(4), s. 041121-1–041121-8. doi: 10.1063/5.0142671. Fulltekst i vitenarkiv Vis sammendrag

  Diffusion of the n-type dopant Sn in β-Ga2O3 is studied using secondary-ion mass spectrometry combined with hybrid functional calculations. The diffusion of Sn from a Sn-doped bulk substrate with surface orientation (001) into an epitaxial layer is observed after heat treatments in the temperature range of 1050–1250 °C. Calculated formation energies of Sn-related and intrinsic defects show that the migration of Sn is mediated by Ga vacancies (VGa) through the formation and dissociation of intermittent mobile VGaSnGa complexes. The evolution of the Sn concentration vs depth profiles after heat treatments can be well described by a reaction–diffusion model. Using model parameters guided by the hybrid functional calculations, we extract a VGaSnGa complex migration barrier of 3.0 ± 0.4 eV with a diffusion coefficient of 2 × 10−1 cm2/s. The extracted migration barrier is consistent with our theoretical predictions using the nudged elastic band method, which shows migration barriers of 3.42, 3.15, and 3.37 eV for the [100], [010], and [001] directions, respectively.

• Polyakov, A.Y.; Kochkova, A.I.; Langørgen, Amanda; Vines, Lasse; Vasilev, A. & Shchemerov, I.V. [Vis alle 8 forfattere av denne artikkelen] (2023). On the possible nature of deep centers in Ga2O3. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. ISSN 0734-2101. 41(2), s. 023401-1–023401-6. doi: 10.1116/6.0002307. Fulltekst i vitenarkiv Vis sammendrag

  The electric field dependence of emission rate of the deep traps with level near Ec−0.6 eV, so-called E1 traps, was studied by means of deep level transient spectroscopy measurements over a wide range of applied voltages. The traps were initially introduced by 900 °C ampoule annealing in molecular hydrogen. The results indicate the activation energy of the centers and the ratio of high-field to low-field electron emission rates at a fixed temperature scale as the square root of electric field, suggesting that the centers behave as deep donors. The possible microscopic nature of the centers in view of recent theoretical calculations is discussed. The most likely candidates for the E1 centers are SiGa1–H or SnGa2–H complexes.

• Seyidov, Palvan; Varley, Joel B.; Frodason, Ymir Kalmann; Klimm, Detlef; Vines, Lasse & Galazka, Zbigniew [Vis alle 10 forfattere av denne artikkelen] (2023). Thermal Stability of Schottky Contacts and Rearrangement of Defects in β-Ga2O3 Crystals. Advanced Electronic Materials. doi: 10.1002/aelm.202300428. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The thermal stability of different Schottky contacts (Au, Pt, and Ni) on (100) β ‐Ga 2 O 3 single crystals grown by the Czochralski method is investigated. Besides the examination of the Schottky barrier parameters, contact‐dependent defect levels are investigated by deep‐level transient spectroscopy (DLTS) in a 100–650 K (ramp‐up) and 650–100 K (ramp‐down) temperature cycle. Several defect levels are detected below the conduction band minimum at 0.41, 0.60, 0.77, 0.96, and 1.17 eV. In the temperature ramp‐down DLTS, the 1.17 eV level disappears, and the 0.60 eV level appears for all Schottky contacts. DFT calculations suggest that rearrangement and dissociation of a single hydrogen from a doubly‐hydrogenated Ga─O divacancy complex occurs during the temperature sweep under bias. The trap level at 0.96 eV only appears after the thermal load for the Ni contact, in contrast to Au and Pt, where it is present without a thermal budget. Temperature‐dependent leakage current (at −4 V) measurements indicate oxidation of Ni, and further thermodynamic analysis suggests alloying of Au‐Ga atoms at the Au/ β ‐Ga 2 O 3 interface. These studies provide insight into the behavior induced by these common Schottky contacts and the alteration associated with temperature cycling.

• Mukhopadhyay, Partha; Hatipoglu, Isa; Frodason, Ymir Kalmann; Varley, Joel Basile; Williams, Martin S. & Hunter, Daniel A. [Vis alle 13 forfattere av denne artikkelen] (2022). Role of defects in ultra-high gain in fast planar tin gallium oxide UV-C photodetector by MBE. Applied Physics Letters. ISSN 0003-6951. 121(11). doi: 10.1063/5.0107557. Fulltekst i vitenarkiv Vis sammendrag

  We report ultra-high responsivity of epitaxial [Formula: see text] (TGO) Schottky UV-C photodetectors and experimentally identified the source of gain as deep-level defects, supported by first principles calculations. Epitaxial TGO films were grown by plasma-assisted molecular beam epitaxy on (−201) oriented n-type β-[Formula: see text] substrates. Fabricated vertical Schottky devices exhibited peak responsivities as high as 3.5 [Formula: see text] A/W at −5 V applied bias under 250 nm illumination with sharp cutoff shorter than 280 nm and fast rise/fall time in milliseconds order. Hyperspectral imaging cathodoluminescence (CL) spectra were examined to find the mid-bandgap defects, the source of this high gain. Irrespective of different tin mole fractions, the TGO epilayer exhibited extra CL peaks at the green band (∼2.20 eV) not seen in β-[Formula: see text] along with enhancement of the blue emission-band (∼2.64 eV) and suppression of the UV emission-band. Based on hybrid functional calculations of the optical emission expected for defects involving Sn in β-[Formula: see text], V Ga –Sn complexes are proposed as potential defect origins of the observed green and blue emission-bands. Such complexes behave as acceptors that can efficiently trap photogenerated holes and are predicted to be predominantly responsible for the ultra-high photoconductive gain in the Sn-alloyed [Formula: see text] devices by means of thermionic emission and electron tunneling. Regenerating the V Ga –Sn defect complexes by optimizing the growth techniques, we have demonstrated a planar Schottky UV-C photodetector of the highest peak responsivity.

• Olsen, Vegard Skiftestad; Frodason, Ymir Kalmann; Hommedal, Ylva Knausgård; Nielsen, Dina Marie; Weiser, Philip Michael & Johansen, Klaus Magnus H [Vis alle 9 forfattere av denne artikkelen] (2022). Li and group-III impurity doping in ZnSnN2: Potential and limitations. PHYSICAL REVIEW MATERIALS. 6(12), s. 1–8. doi: 10.1103/PhysRevMaterials.6.124602. Fulltekst i vitenarkiv Vis sammendrag

  II–IV nitrides and their alloys represent an earth-abundant and potentially cost-efficient alternative to the well-developed AlN-GaN-InN system. A major drawback with the II–IV nitrides is that ZnSnN2, the lowest band gap material, exhibits unfavorably high carrier concentrations for as-grown, stoichiometric material, limiting the material systems potential use in applications such as solar cells and light-emitting diodes. Lithium (Li) has been suggested as a shallow acceptor defect in ZnSnN2 if substituting for Zn, and hence doping with Li has been identified as a possible way to improve the electronic properties. Herein, theoretical calculations by hybrid functional density functional theory have been employed and extended to include defect complexes as well, which to this point remained unexplored. The calculations reveal that even though Li on the Zn site (the LiZn) is an acceptor, the defect may easily complex with the Lii donor, rendering the complex neutral. Our theoretical findings are supported by a Li-doping series of ZnSnN2, where a doping concentration ranging from 2.10×1019cm−3 to 1.85×1020cm−3 was obtained. The n-type carrier concentration was found to be unaffected by the doping concentration, and no systematic change in the absorption onset, probably affected by a Burstein-Moss shift, was observed. Possible group-III dopants, as have been found to yield interesting results for ZnGeN2, such as In, Ga, Al, and B, have also been investigated as an alternative dopant in ZnSnN2.

• Langørgen, Amanda; Zimmermann, Christian; Frodason, Ymir Kalmann; Verhoeven, Espen Førdestrøm; Weiser, Philip Michael & Karsthof, Robert Michael [Vis alle 8 forfattere av denne artikkelen] (2022). Influence of heat treatments in H2 and Ar on the E1 center in β-Ga2O3. Journal of Applied Physics. ISSN 0021-8979. 131(115702). doi: 10.1063/5.0083861. Fulltekst i vitenarkiv Vis sammendrag

  The influence of heat treating [Formula: see text]-type bulk [Formula: see text]-Ga[Formula: see text]O[Formula: see text] in hydrogen (H[Formula: see text]) and argon (Ar) gases on the presence of the defect level commonly labeled as [Formula: see text] was studied. Fourier transform-infrared spectroscopy confirms that hydrogen (H) is incorporated into [Formula: see text]-Ga[Formula: see text]O[Formula: see text] during H[Formula: see text] annealing at 900 °C. Deep-level transient spectroscopy measurements reveal that the concentration of the [Formula: see text] level is promoted by the introduction of H, in contrast to what is observed in samples heat-treated in an Ar flow. We further find the [Formula: see text] level to be stable against heat treatments at 650 K, both with and without an applied reverse-bias voltage. Potential candidates for the defect origin of [Formula: see text] are investigated using hybrid-functional calculations, and three types of defect complexes involving H are found to exhibit charge-state transition levels compatible with [Formula: see text], including substitutional H at one of the threefold coordinated O sites, Ga-substitutional shallow donor impurities passivated by H, and certain configurations of singly hydrogenated Ga–O divacancies. Among these types, only the latter exhibit H binding energies that are consistent with the observed thermal stability of [Formula: see text].

• Karsthof, Robert Michael; Frodason, Ymir Kalmann; Galeckas, Augustinas; Weiser, Philip Michael; Zviagin, Vitaly & Grundmann, Marius (2022). Light Absorption and Emission by Defects in Doped Nickel Oxide. Advanced Photonics Research. ISSN 2699-9293. 3(11). doi: 10.1002/adpr.202200138. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Galeckas, Augustinas; Vines, Lasse & Johansen, Klaus Magnus H (2024). Zn diffusion and luminescence from Zn acceptors in Zn doped β-Ga2O3. Fulltekst i vitenarkiv
• Langørgen, Amanda; Frodason, Ymir Kalmann; Jensen, Ingvild Julie Thue & Vines, Lasse (2024). A metastable deep defect in β-Ga2O3. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Galeckas, Augustinas; Galazka, Zbigniew; Vines, Lasse & Walle, Chris G. Van De (2024). Broad luminescence in single-crystalline ZnGa2O. Fulltekst i vitenarkiv
• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2023). Ge donor diffusion in β-Ga2O3. Fulltekst i vitenarkiv
• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2023). Impurity diffusion in β-Ga2O3. Fulltekst i vitenarkiv
• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2022). Zn diffusion in 𝛽-Ga2O3 using SIMS. Fulltekst i vitenarkiv
• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2022). Diffusion of Zn in beta-Ga2O3. Fulltekst i vitenarkiv
• Hommedal, Ylva Knausgård; Frodason, Ymir Kalmann; Vines, Lasse & Johansen, Klaus Magnus H (2022). Dynamic interaction of Zn and intrinsic defects in beta-Ga2O3. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Varley, Joel Basile; Johansen, Klaus Magnus H; Vines, Lasse & Walle, Chris G. Van de (2022). Strongly anisotropic migration of the Ga vacancy in ß-Ga2O3. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Krzyzaniak, Patryk Piotr; Vines, Lasse; Varley, Joel Basile; Walle, Chris G. Van de & Johansen, Klaus Magnus H (2022). Ga vacancy-mediated diffusion of Sn donors in β-Ga2O3. Fulltekst i vitenarkiv
• Langørgen, Amanda; Frodason, Ymir Kalmann; Karsthof, Robert Michael; Wenckstern, Holger von; Jensen, Ingvild Thue & Vines, Lasse (2022). An electron trap in κ-Ga2O3 and the quest for its microscopic origin. 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
• Langørgen, Amanda; Karsthof, Robert Michael; Weiser, Philip Michael; Cavani, Olivier; Grasset, Romain & Frodason, Ymir Kalmann [Vis alle 8 forfattere av denne artikkelen] (2021). Steady-state Photocapacitance Spectroscopy of Intrinsic Defects in Electron-Irradiated β-Ga₂O₃. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Zimmermann, Christian; Verhoeven, Espen Førdestrøm; Weiser, Philip Michael; Vines, Lasse & Varley, Joel Basile (2021). Multistability of Ga-O divacancies in β-Ga2O3. Fulltekst i vitenarkiv
• Krzyzaniak, Patryk Piotr; Frodason, Ymir Kalmann; Weiser, Philip Michael; Vines, Lasse & Johansen, Klaus Magnus H (2021). Diffusion of donor dopants in β-Ga2O3 and interplay with gallium vacancies. Fulltekst i vitenarkiv
• Zimmermann, Christian; Frodason, Ymir Kalmann; Varley, Joel Basile; Verhoeven, Espen Førdestrøm; Rønning, Vegard & Weiser, Philip Michael [Vis alle 15 forfattere av denne artikkelen] (2021). Identification of Fe-, Ti- and H-related Charge-state Transition Levels in β-Ga2O3. Fulltekst i vitenarkiv
• Krzyzaniak, Patryk Piotr; Vines, Lasse & Johansen, Klaus Magnus H (2021). Development of β-Ga2O3 as a novel material for power electronics, dopant diffusion and defect interaction. Universitetet i Oslo. Fulltekst i vitenarkiv

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