Klaus Magnus Håland Johansen

• 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.

• 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.

• 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.

• 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.

• Borgersen, Jon; Johansen, Klaus Magnus H; Vines, Lasse; Wenckstern, Holger von; Grundmann, Marius & Kuznetsov, Andrej (2021). Fermi level controlled point defect balance in ion irradiated indium oxide. Journal of Applied Physics. ISSN 0021-8979. 130(8). doi: 10.1063/5.0062135. Fulltekst i vitenarkiv Vis sammendrag

  Fermi level controlled point defect balance is demonstrated in ion irradiated indium oxide (In2O3). Specifically, our observations can be sub-divided into the formation of isolated Frenkel pairs and secondary defects, correlated with an increase and decrease in resistance, respectively. Importantly, by considering the net charge contribution from the most energetically stable Frenkel pair configurations, we explain the data trends for low doses and determine an upper limit for the Fermi level pinning. Moreover, by comparing the corresponding number of generated carriers with the ballistic defect generation rates, we estimate the dynamic annealing efficiency. Further irradiation toward higher doses is consistent with the buildup of secondary defects. As such, the present data may be of practical use in a variety of In2O3 device applications requiring predictions of its radiation tolerance. In a broader perspective, the present methodology may be valuable for benchmarking defect simulation data in semiconductors in general.

• Reinertsen, Vilde Mari; Weiser, Philip Michael; Frodason, Ymir Kalmann; Bathen, Marianne Etzelmüller; Vines, Lasse & Johansen, Klaus Magnus H (2020). Anisotropic and trap-limited diffusion of hydrogen/deuterium in monoclinic gallium oxide single crystals. Applied Physics Letters. ISSN 0003-6951. 117. doi: 10.1063/5.0027333. Fulltekst i vitenarkiv Vis sammendrag

  The effect of lattice anisotropy on the diffusion of hydrogen (H)/deuterium (2H) in b-Ga2O3 was investigated using secondary ion mass spectrometry (SIMS) and hybrid-functional calculations. Concentration-depth profiles of 2H-implanted single crystals show that 2H can diffuse along the direction perpendicular to the (010) surface at temperatures as low as 300 degC, whereas diffusion along the direction perpendicular to the (-201) surface occurs only around 500 degC. For both directions, the evolution of the 2H concentration–depth profiles after heat treatments can be modeled by trap-limited diffusion. Moreover, the traps can be present in the as-received crystals or created during ion implantation. Comparison of the experimentally obtained binding energy for 2H to the trap (2.3+/-0.2 eV) with the binding energies determined from first-principles calculations suggests that intrinsic point defects (e.g., VGa^ib) or defect complexes (e.g., VGa(2)VO(2)) are excellent candidates for the trap and will play a crucial role in the diffusion of H or 2H in b-Ga2O3.

• Borgersen, Jon; Vines, Lasse; Frodason, Ymir Kalmann; Kuznetsov, Andrej; Wenckstern, Holger von & Grundmann, Marius [Vis alle 9 forfattere av denne artikkelen] (2020). Experimental exploration of the amphoteric defect model by cryogenic ion irradiation of a range of wide band gap oxide materials. Journal of Physics: Condensed Matter. ISSN 0953-8984. 32(50). doi: 10.1088/1361-648X/abac8b. Fulltekst i vitenarkiv Vis sammendrag

  The evolution of electrical resistance as function of defect concentration is examined for the unipolar n-conducting oxides CdO, β-Ga2O3, In2O3, SnO2 and ZnO in order to explore the predictions of the amphoteric defect model. Intrinsic defects are introduced by ion irradiation at cryogenic temperatures, and the resistance is measured in-situ by current–voltage sweeps as a function of irradiation dose. Temperature dependent Hall effect measurements are performed to determine the carrier concentration and mobility of the samples before and after irradiation. After the ultimate irradiation step, the Ga2O3 and SnO2 samples have both turned highly resistive. In contrast, the In2O3 and ZnO samples are ultimately found to be less resistive than prior to irradiation, however, they both show an increased resistance at intermediate doses. Based on thermodynamic defect charge state transitions computed by hybrid density functional theory, a model expanding on the current amphoteric defect model is proposed.

• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Vines, Lasse & Varley, J.B. (2020). Self-trapped hole and impurity-related broad luminescence in β-Ga2O3. Journal of Applied Physics. ISSN 0021-8979. 127(7). doi: 10.1063/1.5140742. Fulltekst i vitenarkiv Vis sammendrag

  This work explores the luminescence properties of self-trapped holes and impurity-related acceptors using one-dimensional configuration coordinate diagrams derived from hybrid functional calculations. The photoluminescence spectrum of as-grown β-Ga2O3 typically consists of a broad band in the wavelength region from ultraviolet to green and is often dominated by an impurity independent ultraviolet band that is commonly attributed to self-trapped holes. Here, we use the self-trapped hole as a benchmark to evaluate the accuracy of the theoretical defect luminescence spectra and estimate the optical properties of MgGa, BeGa, CaGa, CdGa, ZnGa, LiGa, and NO acceptor impurities, as well as their complexes with hydrogen donors. We also explore VGa acceptors complexed with hydrogen and SiGa donor impurities. The results show that these defects can give rise to broad luminescence bands peaking in the infrared to visible part of the spectrum, making them potential candidates for the defect origin of broad luminescence bands in β-Ga2O3.

• Vasquez, Geraldo Cristian; Johansen, Klaus Magnus H; Galeckas, Augustinas; Vines, Lasse & Svensson, Bengt Gunnar (2020). Optical signatures of single ion tracks in ZnO. Nanoscale Advances. 2(2), s. 724–733. doi: 10.1039/C9NA00677J. Fulltekst i vitenarkiv Vis sammendrag

  The optical properties of single ion tracks have been studied in ZnO implanted with Ge by combining depth-resolved hyperspectral cathodoluminescence (CL) and photoluminescence (PL) spectroscopy techniques. The results indicate that ZnO is susceptible to implantation doses as low as 108 to 109 cm−2. We demonstrate that the intensity ratio of ionized and neutral donor bound exciton emissions [D+X/D0X] can be used as a tracer for a local band bending both at the surface as well as in the crystal bulk along the ion tracks. The hyperspectral CL imaging performed at 80 K with 50 nm resolution over the regions with single ion tracks permitted direct assessment of the minority carrier diffusion length. The radii of distortion and space charge surrounding single ion tracks were estimated from the 2D distributions of defect-related green emission (GE) and excitonic D+X emission, both normalized with regard to neutral D0X emission, i.e., from the [GE/D0X] and [D+X/D0X] ratio maps. Our results indicate that single ion tracks in ZnO can be resolved up to ion doses of the order of 5 × 109 cm−2, in which defect aggregation along the extended defects obstructs signatures of individual tracks.

• Vasquez, Geraldo Cristian; Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Bazioti, Kalliopi; Johansen, Klaus Magnus H & Maestre, D. [Vis alle 11 forfattere av denne artikkelen] (2020). Strain Modulation of Si Vacancy Emission from SiC Micro- and Nanoparticles. Nano Letters. ISSN 1530-6984. 20(12), s. 8689–8695. doi: 10.1021/acs.nanolett.0c03472. Fulltekst i vitenarkiv Vis sammendrag

  Single-photon emitting point defects in semiconductors have emerged as strong candidates for future quantum technology devices. In the present work, we exploit crystalline particles to investigate relevant defect localizations, emission shifting, and waveguiding. Specifically, emission from 6H-SiC micro- and nanoparticles ranging from 100 nm to 5 μm in size is collected using cathodoluminescence (CL), and we monitor signals attributed to the Si vacancy (VSi) as a function of its location. Clear shifts in the emission wavelength are found for emitters localized in the particle center and at the edges. By comparing spatial CL maps with strain analysis carried out in transmission electron microscopy, we attribute the emission shifts to compressive strain of 2–3% along the particle a-direction. Thus, embedding VSi qubit defects within SiC nanoparticles offers an interesting and versatile opportunity to tune single-photon emission energies while simultaneously ensuring ease of addressability via a self-assembled SiC nanoparticle matrix.

• Schifano, Ramon; Jakiela, R; Galeckas, Augustinas; Kopalko, K; Herklotz, Frank & Johansen, Klaus Magnus H [Vis alle 7 forfattere av denne artikkelen] (2019). Role of intrinsic and extrinsic defects in H implanted hydrothermally grown ZnO. Journal of Applied Physics. ISSN 0021-8979. 126(12). doi: 10.1063/1.5115597. Fulltekst i vitenarkiv Vis sammendrag

  The impact of hydrogen in ZnO is revealed by combining reaction dynamics calculations with temperature dependent Hall (TDH), photoluminescence, and secondary ion mass spectrometry measurements performed on H, 2H, and He implanted ZnO. H and 2H box profiles with a concentration ranging from ∼3×1017 cm−3 to ∼1019 cm−3 and He to produce as much as damage as in the [H] ∼3×1017 cm−3 case were implanted in the samples. The formation of Li lean regions has been observed for [2H] <1019 cm−3 after annealing at 400 ∘C. This is attributed to Lii presence consequent to the diffusion of Zni created during the H/2H implantation process. Results extracted from the TDH measurements performed prior to the annealing at 400 ∘C evidence that Lii contributes to an increase in carrier concentration up to ∼1017 cm−3 by providing a donor level with an activation energy of ∼40 meV and thus is very close to the value of ∼47 meV expected for H in the oxygen site. The reaction dynamics analysis evidences that the amount of Lii introduced is decreasing at higher H implantation doses as a result of increasing VZn and H-VZn retrapping, reactions in which Lii is competing with H. Overall, due to Lii formation as well as the presence of Al the maximum percentage of the implanted H or 2H acting as a donor in the investigated range is found to be ≲ 2%, which is considerably lower than previously reported.

• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Galeckas, Augustinas & Vines, Lasse (2019). Broad luminescence from donor-complexed LiZn and NaZn acceptors in ZnO. Physical review B (PRB). ISSN 2469-9950. 100(18). doi: 10.1103/PhysRevB.100.184102. Fulltekst i vitenarkiv Vis sammendrag

  Zn substitutional lithium ( Li Zn ) and sodium ( Na Zn ) acceptors and their complexes with common donor impurities ( Al Zn , Hi, and HO) in ZnO have been studied using hybrid functional calculations. The results show that the complexes are not exclusively charge neutral, but rather exhibit a thermodynamic ( + / 0 ) transition level close to the valence band maximum. The positive charge states are associated with a polaronic defect state, similar to those of the well-studied charge-neutral isolated acceptors. This incomplete passivation has profound consequences for the optical properties of the complexes. Indeed, electron transitions from the conduction band minimum to the ( + / 0 ) transition level of the complexes result in broad luminescence bands that are blueshifted with respect to those originating from the isolated acceptors. Such complexes are proposed as a potential defect origin of the green luminescence observed at the high-energy side of the orange luminescence band (caused by Li Zn ) in hydrothermally grown ZnO. This prediction is supported by experimental photoluminescence and secondary ion mass spectrometry data on a hydrothermally grown ZnO sample. We have also explored how the parameters controlling the fraction and screening of exchange in the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional influence the results by comparing two parametrization approaches: (i) the conventional one where the exchange fraction is adjusted to reproduce the experimental band gap, and (ii) tuning both parameters in order to also comply with the generalized Koopmans theorem (gKT). Interestingly, these approaches were found to yield similar results.

• Zhan, Wei; Kosinskiy, Andrey; Vines, Lasse; Johansen, Klaus Magnus H; Carvalho, Patricia Almeida & Prytz, Øystein (2019). ZnCr2O4 Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS. Materials. 12. doi: 10.3390/ma12060888. Fulltekst i vitenarkiv Vis sammendrag

  The ZnCr2O4/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr2O4) particles. Ball-milled and dry-pressed ZnO and chromium oxide (α-Cr2O3) powder formed ZnCr2O4 inclusions in ZnO with size ~400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [2 1¯1¯ 3]/ZnCr2O4 [1 1¯ 0] orientations, while ZnO [1 2¯ 10]/ZnCr2O4 [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr2O4 nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr2O4 nanoparticles was measured to be 3.84 ± 0.03 eV, in contrast to 3.22 ± 0.01 eV for the ZnO matrix.

• Sky, Thomas Neset; Johansen, Klaus Magnus H; Frodason, Ymir Kalmann; Aarholt, Thomas; Riise, Heine Nygard & Prytz, Øystein [Vis alle 8 forfattere av denne artikkelen] (2019). Diffusion of indium in single crystal zinc oxide: a comparison between group III donors. Semiconductor Science and Technology. ISSN 0268-1242. 34(2), s. 1–6. doi: 10.1088/1361-6641/aafa4c. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Alkauskas, A & Vines, Lasse (2019). Negative- U and polaronic behavior of the Zn-O divacancy in ZnO. Physical review B (PRB). ISSN 2469-9950. 99(17), s. 1–7. doi: 10.1103/PhysRevB.99.174106. Fulltekst i vitenarkiv
• Bazioti, Kalliopi; Azarov, Alexander; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar; Vines, Lasse & Kuznetsov, Andrej [Vis alle 7 forfattere av denne artikkelen] (2019). Role of Nitrogen in Defect Evolution in Zinc Oxide: STEM−EELS Nanoscale Investigations. The Journal of Physical Chemistry Letters. 10(16), s. 4725–4730. doi: 10.1021/acs.jpclett.9b01472. Fulltekst i vitenarkiv Vis sammendrag

  Direct evidence of the formation of nitrogen molecules (N2) after ion implantion of ZnO has been revealed by an atomically resolved scanning transmission electron microscopy (STEM)–electron energy-loss spectroscopy (EELS) investigation. Taking advantage of the possibility of using multiple detectors simultaneously in aberration-corrected STEM, we utilize the detailed correlation between the atomic structure and chemical identification to develop a model explaining the formation and evolution of different defect types and their interaction with N. In particular, the formation of zinc vacancy (VZn) clusters filled with N2 after heat treatment at 650 °C was observed, clearly indicating that N has not been stabilized in the O substitution site, thus limiting p-type doping. Previous results showing an exceptional thermal stability of vacancy clusters only for the case of N-doped ZnO are supported. Furthermore, VZn–N2 stabilization leads to suppression of VZn–Zni recombination; hence, the highly mobile Zn interstitials preferentially condense on the basal planes promoting formation of extended defects (basal stacking faults and stacking mismatched boundaries). The terminations of these defects provide energetically favorable sites for further N2 trapping as a way to reduce local strain fields.

• Sky, Thomas Neset; Johansen, Klaus Magnus H; Riise, Heine Nygard; Svensson, Bengt Gunnar & Vines, Lasse (2018). Gallium diffusion in zinc oxide via the paired dopant-vacancy mechanism. Journal of Applied Physics. ISSN 0021-8979. 123(5). doi: 10.1063/1.5000123. Fulltekst i vitenarkiv Vis sammendrag

  Isochronal and isothermal diffusion experiments of gallium (Ga) in zinc oxide (ZnO) have been performed in the temperature range of 900–1050 °C. The samples used consisted of a sputter-deposited and highly Ga-doped ZnO film at the surface of a single-crystal bulk material. We use a novel reaction diffusion (RD) approach to demonstrate that the diffusion behavior of Ga in ZnO is consistent with zinc vacancy (VZn) mediation via the formation and dissociation of GaZnVZn complexes. In the RD modeling, experimental diffusion data are fitted utilizing recent density-functional-theory estimates of the VZn formation energy and the binding energy of GaZnVZn. From the RD modeling, a migration energy of 2.3 eV is deduced for GaZnVZn, and a total/effective activation energy of 3.0 eV is obtained for the Ga diffusion. Furthermore, and for comparison, employing the so-called Fair model, a total/effective activation energy of 2.7 eV is obtained for the Ga diffusion, reasonably close to the total value extracted from the RD-modeling. © 2018 AIP Publishing

• Sky, Thomas Neset; Johansen, Klaus Magnus H; Frodason, Ymir Kalmann; Svensson, Bengt Gunnar & Vines, Lasse (2018). The interaction between lithium acceptors and gallium donors in zinc oxide. Journal of Applied Physics. ISSN 0021-8979. 124(24), s. 1–6. doi: 10.1063/1.5063326. Fulltekst i vitenarkiv Vis sammendrag

  Diffusion of lithium (Li) in uniformly gallium (Ga)-doped monocrystalline bulk Zinc Oxide (ZnO) is studied over a wide temperature range (500 − 1150◦C) and is demonstrated to be dictated by the distribution of Ga. Below 800◦C, the indiffusion of Li from a Li-doped ZnO sputtered film into a n + ZnO bulk yields an abrupt and compensated Li-doped box region with the Li concentration matching the free-electron concentration, in accordance with several previous experimental and theoretical reports. However, experimental observations of Li-diffusion at higher temperatures have not previously been reported. In this study we give a detailed description of a dissociative diffusion mechanism for Li up to 1150◦C. By employing a reaction-diffusion model that accounts for the presence of both Li and Ga, a dissociation energy of 4.6 eV with an attempt frequency of 5×1015s −1 is obtained from the experimental Li diffusion data. This is in excellent agreement with theoretical results for the dissociation of (LiZnGaZn) 0 (4.8 eV) into Li+ i and (GaZnVZn) −, and strongly suggest that this neutral and stable acceptor-donor pair prevails in Li- and Ga-doped ZnO.

• Sky, Thomas Neset; Johansen, Klaus Magnus H; Venkatachalapathy, Vishnukanthan; Svensson, Bengt Gunnar; Tuomisto, Filip & Vines, Lasse (2018). Influence of Fermi level position on vacancy-assisted diffusion of aluminum in zinc oxide. Physical review B (PRB). ISSN 2469-9950. 98(24), s. 245204-1–245204-8. doi: 10.1103/PhysRevB.98.245204. Fulltekst i vitenarkiv Vis sammendrag

  The influence of Fermi level position and annealing ambient on the zinc vacancy VZn generation and Al diffusion is studied in monocrystalline zinc oxide (ZnO). From secondary-ion mass spectrometry and positron annihilation spectroscopy results, a quadratic dependence between the concentrations of VZn and Al is established, demonstrating the Fermi level dependence of the formation of the electrically compensating −2 charge state of VZn in conductive n-type ZnO crystals. In contrast, thermal treatment in the zinc-rich ambient is shown to efficiently reduce the VZn concentration and related complexes. Using a reaction-diffusion model, the diffusion characteristics of Al at different donor background concentrations are fully accounted for by mobile (AlZnVZn)− pairs. These pairs form via the migration and reaction of isolated V2−Zn with the essentially immobile Al+Zn. We obtain a migration barrier for the (AlZnVZn)− pair of 2.4±0.2 eV, in good agreement with theoretical predictions. In addition to strongly alter the shape of the Al diffusion profiles, increasing the donor background concentration also results in an enhanced effective Al diffusivity, attributed to a reduction in the V2−Zn formation energy as the Fermi level position increases.

• Granerød, Cecilie Skjold; Bilden, Sindre Rannem; Aarholt, Thomas; Yao, Yu-Feng; Yang, C. C. & Look, David C. [Vis alle 9 forfattere av denne artikkelen] (2018). Direct observation of conduction band plasmons and the related Burstein-Moss shift in highly doped semiconductors: A STEM-EELS study of Ga-doped ZnO. Physical review B (PRB). ISSN 2469-9950. 98(11). doi: 10.1103/PhysRevB.98.115301. Fulltekst i vitenarkiv Vis sammendrag

  The combination of high optical transparency and low electrical resistivity has made transparent conductive oxides (TCOs) a key technology in many optoelectronic applications. Furthermore, the study of TCOs yields insight into many fundamental parameters of semiconductors. For example, the high charge carrier concentration results in an apparent shift in the band gap, the so-called Burstein-Moss shift, in addition to plasmonic resonances in the near infrared regime. While both effects are related to the carrier concentration and band structure, their lateral distribution and interaction with boundary conditions such as interfaces and surfaces are difficult to assess, and a direct observation of the local distribution has remained elusive. Here we employ electron energy-loss spectroscopy in scanning transmission electron microscopy (STEM-EELS) for direct observation of spatially resolved plasmonic resonances and Burstein-Moss shift in gallium doped zinc oxide (GZO), one of the most widely used TCOs. A 25 nm thick GZO film with a carrier concentration of 7× 10 20 cm − 3 has been grown epitaxially on a nominally undoped ZnO film. The GZO film shows a renormalized Burstein-Moss shift of ∼ 0.5 eV, in accordance with that expected from Hall effect measurements. The plasma resonance of the conduction band electrons is located at 0.82 eV in the bulk GZO, and with a substantial increase in intensity towards the sample surface, where a surface plasmon energy of 0.54 eV is observed. Hence we have directly measured differences in optical properties between the two films, the local variation across the GZO film has been studied, and we are also directly observing the difference between bulk and surface properties of GZO. © 2018 American Physical Society

• Granerød, Cecilie Skjold; Galeckas, Augustinas; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2018). The temperature-dependency of the optical band gap of ZnO measured by electron energy-loss spectroscopy in a scanning transmission electron microscope. Journal of Applied Physics. ISSN 0021-8979. 123(14), s. 1–6. doi: 10.1063/1.5023316. Fulltekst i vitenarkiv Vis sammendrag

  The optical band gap of ZnO has been measured as a function of temperature using Electron Energy-Loss Spectroscopy (EELS) in a (Scanning) Transmission Electron Microscope ((S)TEM) from approximately 100 K up towards 1000 K. The band gap narrowing shows a close to linear dependency for temperatures above 250 K and is accurately described by Varshni, Bose-Einstein, Pässler and Manoogian-Woolley models. Additionally, the measured band gap is compared with both optical absorption measurements and photoluminescence data. STEM-EELS is here shown to be a viable technique to measure optical band gaps at elevated temperatures, with an available temperature range up to 1500 K and the benefit of superior spatial resolution. © 2018 AIP Publishing

• Jensen, Ingvild Julie Thue; Johansen, Klaus Magnus H; Zhan, Wei; Venkatachalapathy, Vishnukanthan; Brillson, Len & Kuznetsov, Andrej [Vis alle 7 forfattere av denne artikkelen] (2018). Bandgap and band edge positions in compositionally graded ZnCdO. Journal of Applied Physics. ISSN 0021-8979. 124(1), s. 015302-1–015302-8. doi: 10.1063/1.5036710. Fulltekst i vitenarkiv Vis sammendrag

  Introducing Cd into ZnO allows for bandgap engineering, potentially with particularly interesting properties to observe in compositionally graded samples. In this work, compositionally graded Zn1–xCdxO samples with 0 ≤ x < 0.16 were made using metal organic vapour phase epitaxy. The chemical composition was studied using scanning transmission electron microscopy, while the band structure of the samples was investigated using a combination of cathodoluminescence spectroscopy and X-ray photoelectron spectroscopy (XPS). It is found that the reduction of the bandgap in our samples is caused by changes in the conduction band. The position of the Fermi level relative to the vacuum level, i.e., the workfunction, was also found to change upon addition of Cd, giving an apparent shift in the valence band when evaluated from the XPS valence spectra. © 2018 AIP Publishing

• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Svensson, Bengt Gunnar & Alkauskas, Audrius (2018). Zn vacancy-donor impurity complexes in ZnO. Physical review B (PRB). ISSN 2469-9950. 97(10), s. 1–8. doi: 10.1103/PhysRevB.97.104109. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Svensson, Bengt Gunnar & Alkauskas, Audrius (2017). Zn vacancy as a polaronic hole trap in ZnO. Physical review B (PRB). ISSN 2469-9950. 95(9). doi: 10.1103/PhysRevB.95.094105. Fulltekst i vitenarkiv
• Zhan, Wei; Granerød, Cecilie Skjold; Venkatachalapathy, Vishnukanthan; Johansen, Klaus Magnus H; Jensen, Ingvild Julie Thue & Kuznetsov, Andrej [Vis alle 7 forfattere av denne artikkelen] (2017). Nanoscale mapping of optical band gaps using monochromated Electron Energy Loss Spectroscopy. Nanotechnology. ISSN 0957-4484. 28(10). doi: 10.1088/1361-6528/aa5962. Fulltekst i vitenarkiv Vis sammendrag

  Using monochromated electron energy loss spectroscopy in a probe-corrected scanning transmission electron microscope we demonstrate band gap mapping in ZnO/ZnCdO thin films with a spatial resolution below 10 nm and spectral precision of 20 meV.

• Prozheeva, V; Johansen, Klaus Magnus H; Neuvonen, Pekka Tapio; Zubiaga, A; Vines, Lasse & Kuznetsov, Andrej [Vis alle 7 forfattere av denne artikkelen] (2017). Subsurface damage in polishing?annealing processed ZnO substrates. Materials Science in Semiconductor Processing. ISSN 1369-8001. 69, s. 19–22. doi: 10.1016/j.mssp.2017.02.021. Fulltekst i vitenarkiv
• Herklotz, Frank; Johansen, Klaus Magnus H; Galeckas, Augustinas; Sky, Thomas Neset & Svensson, Bengt Gunnar (2016). The influence of Fe impurities on the annealing of OH–Li complexes in ZnO. Physica status solidi (b). ISSN 0370-1972. 253(2), s. 273–278. doi: 10.1002/pssb.201552441. Fulltekst i vitenarkiv
• Ruane, W.T.; Johansen, Klaus Magnus H; Leedy, K. D.; Look, David C.; Wenckstern, H Von & Grundmann, Michael [Vis alle 8 forfattere av denne artikkelen] (2016). Defect segregation and optical emission in ZnO nano- and microwires. Nanoscale. ISSN 2040-3364. 8(14), s. 7631–7637. doi: 10.1039/c5nr08248j. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Tuomisto, Filip; Makkonen, Ilja & Vines, Lasse (2016). Formation of Zn- and O- vacancy clusters in ZnO through deuterium annealing. Materials Science in Semiconductor Processing. ISSN 1369-8001. 69, s. 23–27. doi: 10.1016/j.mssp.2016.11.030. Fulltekst i vitenarkiv Vis sammendrag

  Open volume defects, clearly distinguishable from the isolated Zn-vacancy are observed in hydrothermally grown ZnO after exposure to deuterium gas at elevated temperatures. From a combination of secondary ion mass spectrometry (SIMS), positron annihilation spectroscopy (PAS) and density functional theory (DFT) calculations it is found that as a result of this treatment vacancy clusters consisting of minimum one Zn- and one O-vacancy are formed, in contrast to introduction of isolated O-vacancies. A scenario for the cluster formation is proposed, where Zn- and O-vacancies originate from the bulk of the sample and the sample surface, respectively. A fraction of the vacancy clusters are decorated by Li and/or H and may therefore be indirectly observed by SIMS. The peak in Li-concentration at about 100 nm below the sample surface, as observed by SIMS is in good correspondence with the PAS-results.

• Herklotz, Frank; Hupfer, Alexander; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar; Koch, Sascha G. & Lavrov, E.V. (2015). Infrared absorption on a complex comprising three equivalent hydrogen atoms in ZnO. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 92(15). doi: 10.1103/PhysRevB.92.155203. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Vines, Lasse; Bjørheim, Tor Svendsen; Schifano, Ramon & Svensson, Bengt Gunnar (2015). Aluminum migration and intrinsic defect interaction in single-crystal zinc oxide. Physical Review Applied. 3:024003(2), s. 1–12. doi: 10.1103/PhysRevApplied.3.024003. Fulltekst i vitenarkiv Vis sammendrag

  Vacancy-mediated migration of Al in single-crystal zinc oxide (ZnO) is investigated using secondary-ion mass spectrometry (SIMS) combined with hybrid density-functional theory (DFT) calculations. A thin film of Al-doped ZnO is deposited by sputtering onto the single-crystal bulk material and heat treated at temperatures in the range of 900 °C–1300 °C. The migration of Al is found to be Zn-vacancy mediated. In order to elucidate the physical processes involved, an alternative model based on reactive diffusion is developed. The model includes the time evolution of the concentration of Al atoms on the Zn site (AlZn), Zn vacancies (vZn), and a complex between the two, where the influence of the charge state of vZn on its formation energy is incorporated through the free carrier concentration. The modeling results exhibit close agreement with the experimental data and the AlZnvZn complex is found to diffuse with an activation energy of 2.6 eV and a preexponential factor of 4×10−2  cm2 s−1. The model is supported by the results from hybrid DFT calculations combined with thermodynamical modeling, which also suggest that a complex between AlZn and vZn is promoted in n-doped material. The charge state of this complex is effectively −1, and it thus acts as a compensating acceptor, limiting full utilization of the shallow AlZn donor. Furthermore, the DFT calculations also predict a high formation energy for both substitutional Al on the O site (AlO) and interstitial Al (Ali), and are therefore of minor importance for Al migration in ZnO. The close coupling between the hybrid DFT calculations and the developed diffusion model enable benchmarking of the accuracy of several parameters extracted from the DFT calculations. Furthermore, since the diffusion model hinges strongly on defect concentrations, it couples directly to results from measurements by other experimental techniques than those used in this paper and provides an opportunity for independent verification of the estimated values by future studies. © 2015 American Physical Society

• Stehr, J. E.; Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Vines, Lasse; Svensson, Bengt Gunnar & Chen, W. M. [Vis alle 7 forfattere av denne artikkelen] (2014). Zinc-Vacancy–Donor Complex: A Crucial Compensating Acceptor in ZnO. Physical Review Applied. 2(2), s. 021001–021001. doi: 10.1103/PhysRevApplied.2.021001. Fulltekst i vitenarkiv Vis sammendrag

  The aluminum–zinc-vacancy (AlZn−VZn) complex is identified as one of the dominant defects in Al-containing n-type ZnO after electron irradiation at room temperature with energies above 0.8 MeV. The complex is energetically favorable over the isolated VZn, binding more than 90% of the stable VZn’s generated by the irradiation. It acts as a deep acceptor with the (0/−) energy level located at approximately 1 eV above the valence band. Such a complex is concluded to be a defect of crucial and general importance that limits the n-type doping efficiency by complex formation with donors, thereby literally removing the donors, as well as by charge compensation. © 2014 American Physical Society

• Chan, K.-S.; Vines, Lasse; Johansen, Klaus Magnus H; Monakhov, Edouard; Ye, J.D & Parkinson, P [Vis alle 9 forfattere av denne artikkelen] (2013). Defect formation and thermal stability of H in high dose H implanted ZnO. Journal of Applied Physics. ISSN 0021-8979. 114(8). doi: 10.1063/1.4819216. Fulltekst i vitenarkiv Vis sammendrag

  We studied the structural properties, defect formation, and thermal stability of H in hydrothermally grown ZnO single crystals implanted with H- dose ranging from 2.5×1016 to 1×1017 cm−2. H implantation is found to create deformed layers with a uniaxial strain of 0.5–2.4% along the c-axis in ZnO, for the low and high dose, respectively. About 0.2–0.4% of the original implanted H concentration can still be detected in the samples by secondary ion mass spectrometry after annealing at a temperature up to 800 °C. The thermally stable H is tentatively attributed to H related defect complexes involving the substitutional H that are bound to O vacancies and/or the highly mobile interstitial H that are bound to substitutional Li occupying Zn vacancies as the samples are cooled slowly from high temperature annealing. H implantation to a dose of 1×1017 cm−2 and followed by annealing at 800 °C, is found to result in the formation of vacancy clusters that evolved into faceted voids with diameter varying from 2 to 30 nm. The truncations around the voids form more favorably on the O-terminated surface than on the Zn-terminated surface, suggesting that O is a preferred surface polarity for the internal facets of the voids in the presence of H. This research was originally published in the Journal of Applied Physics. © AIP Publishing

• Zhang, Z.; Look, D. C.; Schifano, Ramon; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar & Brillson, L.J. (2013). Process dependence of H passivation and doping in H-implanted ZnO. Journal of Physics D: Applied Physics. ISSN 0022-3727. 46(5). doi: 10.1088/0022-3727/46/5/055107. Fulltekst i vitenarkiv
• Knutsen, Knut Erik; Johansen, Klaus Magnus H; Neuvonen, Pekka Tapio; Svensson, Bengt Gunnar & Kuznetsov, Andrej (2013). Diffusion and configuration of Li in ZnO. Journal of Applied Physics. ISSN 0021-8979. 113(2). doi: 10.1063/1.4773829. Fulltekst i vitenarkiv Vis sammendrag

  Diffusion of Li into ZnO from an “infinite” surface source under oxygen-rich conditions is studied using secondary ion mass spectrometry. The Li concentration-versus-depth profiles exhibit a distinct and sharp drop, which evolves in position with temperature and time. The sharp drop is associated with an efficient conversion from highly mobile Li-interstitials (Lii) to practically immobile Li-substitutionals (LiZn) via a kick-out mechanism. The characteristic concentration level at which Li drops provides a measure of the active donor concentration in the samples at the processing temperature, and gives evidence of residual impurities being responsible for the commonly observed “native” n-type conductivity. These donors are suggested to arise from different impurities, with Al and Si as the prevailing ones in hydrothermal and melt grown material. Further, evidence of electric field effects on Li diffusion profiles is obtained, and they are considered as a main reason for the slow diffusivity obtained in this work (using O-rich conditions) relative to those previously reported in the literature (obtained under Zn-rich conditions). This research was originally published in the Journal of Applied Physics. © AIP Publishing

• Bjørheim, Tor Svendsen; Erdal, Skjalg; Johansen, Klaus Magnus H; Knutsen, Knut Erik & Norby, Truls (2012). H and Li Related Defects in ZnO and Their Effect on Electrical Properties. Journal of Physical Chemistry C. ISSN 1932-7447. 116(44), s. 23764–23772. doi: 10.1021/jp307835c. 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
• 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
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Azarov, Alexander; Johansen, Klaus Magnus H; Kuznetsov, Andrej & Vines, Lasse [Vis alle 7 forfattere av denne artikkelen] (2021). Thermal evolution of point and extended defects in N-implanted ZnO and (ZnO)1−x(GaN)x thin films: STEM-EELS investigations. 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
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Azarov, Alexander; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar & Kuznetsov, Andrej [Vis alle 8 forfattere av denne artikkelen] (2020). Role of nitrogren in defect evolution in ZnO and (ZnO)₁−ₓ(GaN)ₓ: STEM-EELS nanoscale investigations. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Galeckas, Augustinas & Vines, Lasse (2019). Optical properties of donor-complexed Li_Zn in ZnO. Fulltekst i vitenarkiv
• Vasquez, Geraldo Cristian; Galeckas, Augustinas; Johansen, Klaus Magnus H; Vines, Lasse & Svensson, Bengt Gunnar (2019). Optical and electrical properties of single ion-tracks in crystalline SiC. Fulltekst i vitenarkiv
• Vasquez, Geraldo Cristian; Bazioti, Kalliopi; Galeckas, Augustinas; Johansen, Klaus Magnus H; Granerød, Cecilie Skjold & Nguyen, Phuong Dan [Vis alle 8 forfattere av denne artikkelen] (2019). Luminescent properties of Zn2GeO4 nanoparticles embedded in ZnO. Fulltekst i vitenarkiv
• Borgersen, Jon; Johansen, Klaus Magnus H; Vines, Lasse; Kuznetsov, Andrej; Frodason, Ymir Kalmann & Wenckstern, Holger von [Vis alle 9 forfattere av denne artikkelen] (2019). Electrical properties of intrinsic defects in wide band gap oxides. Fulltekst i vitenarkiv
• Borgersen, Jon; Vines, Lasse; Johansen, Klaus Magnus H; Kuznetsov, Andrej; Wenckstern, Holger von & Perez, Jesus Zuniga [Vis alle 7 forfattere av denne artikkelen] (2019). Using intrinsic defects as dopants in wide band gap semiconducting oxides. Fulltekst i vitenarkiv
• Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Johansen, Klaus Magnus H; Azarov, Alexander; Kuznetsov, Andrej & Vines, Lasse [Vis alle 7 forfattere av denne artikkelen] (2019). Transmission Electron Microscopy methods for atomic-scale investigations of semiconductor properties. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Vines, Lasse & Svensson, Bengt Gunnar (2018). Hybrid functional study of the Zn-O divacancy in ZnO. Fulltekst i vitenarkiv
• Vasquez, Geraldo Cristian; Johansen, Klaus Magnus H; Galeckas, Augustinas; Vines, Lasse; Svensson, Bengt Gunnar & Maestre, David (2018). Single ion-tracks in crystalline ZnO and their influence on the near band edge luminescence. Fulltekst i vitenarkiv
• Zhan, Wei; Granerød, Cecilie Skjold; Venkatachalapathy, Vishnukanthan; Johansen, Klaus Magnus H; Jensen, Ingvild Julie Thue & Kuznetsov, Andrej [Vis alle 7 forfattere av denne artikkelen] (2018). Reply to Comment on 'Nanoscale mapping of optical band gaps using monochromated electron energy loss spectroscopy'. Nanotechnology. ISSN 0957-4484. 29(31). doi: 10.1088/1361-6528/aac3ed. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Bergum, Kristin; Riise, Heine Nygard & Grini, Sigbjørn (2017). Advanced characterization of solar energy materials and novel solar cell concepts. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H (2017). Defects in ZnO by cathodoluminescence spectroscopy possibilities and pitfalls. Fulltekst i vitenarkiv
• Bathen, Marianne Etzelmüller; Borgersen, Jon Arthur; Grini, Sigbjørn; Johansen, Klaus Magnus H; Nyborg, Martin & Olsen, Vegard Skiftestad [Vis alle 7 forfattere av denne artikkelen] (2017). Omvisning FAM. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Sky, Thomas Neset; Frodason, Ymir Kalmann; Venkatachalapathy, Vishnukanthan; Svensson, Bengt Gunnar & Vines, Lasse (2017). Tailoring donor diffusion in ZnO by defects and doping. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H & Vasquez, Geraldo Cristian (2017). Cathodoluminescence characterization of semiconducting oxides. Fulltekst i vitenarkiv
• Sky, Thomas Neset; Johansen, Klaus Magnus H; Vines, Lasse; Svensson, Bengt Gunnar & Riise, Heine Nygard (2017). Diffusion of Al in ZnO: the interplay with Zn-vacancies. Fulltekst i vitenarkiv
• Riise, Heine Nygard; Bathen, Marianne Etzelmüller; Borgersen, Jon Arthur; Grini, Sigbjørn & Johansen, Klaus Magnus H (2017). Besøk frå Nanoskolen 2017. Fulltekst i vitenarkiv
• Sky, Thomas Neset; Johansen, Klaus Magnus H; Vines, Lasse; Svensson, Bengt Gunnar & Riise, Heine Nygard (2017). Diffusion of Group III Elements in ZnO. Fulltekst i vitenarkiv
• Vines, Lasse; Sky, Thomas Neset; Johansen, Klaus Magnus H & Svensson, Bengt Gunnar (2017). Self-compensation and the vacancy-dopant pair in highly Al- and Ga-doped ZnO. Fulltekst i vitenarkiv
• Granerød, Cecilie Skjold; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2017). The temperature-dependency of the ZnO band gap measured by STEM-EELS. Fulltekst i vitenarkiv
• Granerød, Cecilie Skjold; Galeckas, Augustinas; Vines, Lasse; Johansen, Klaus Magnus H & Prytz, Øystein (2017). Temperature-dependency of the ZnO band gap measured by STEM-EELS. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Svensson, Bengt Gunnar & Alkauskas, Audrius (2017). Luminescence from Zn vacancy-donor complexes in ZnO. Fulltekst i vitenarkiv
• Granerød, Cecilie Skjold; Galeckas, Augustinas; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2017). The temperature-dependency of the ZnO bandgap studied by STEM-EELS. Fulltekst i vitenarkiv
• Granerød, Cecilie Skjold; Bilden, Sindre Rannem; Zhan, Wei; Vines, Lasse; Johansen, Klaus Magnus H & Prytz, Øystein (2017). Measuring the ZnO bandgap and its temperature dependency with STEM-EELS. Fulltekst i vitenarkiv
• Borgersen, Jon Arthur; Johansen, Klaus Magnus H & Kuznetsov, Andrej (2017). Characterisation of the specific contact resistance to indium oxides. Fulltekst i vitenarkiv
• Grini, Sigbjørn; Ross, Nils; Johansen, Klaus Magnus H; Platzer-Björkman, Charlotte; Persson, Clas & Vines, Lasse (2016). CZTS solar cells: Band gap grading by selenium diffusion. Fulltekst i vitenarkiv
• Granerød, Cecilie Skjold; Zhan, Wei; Johansen, Klaus Magnus H; Vines, Lasse & Prytz, Øystein (2016). Band gap measurements by STEM EELS. Fulltekst i vitenarkiv
• Granerød, Cecilie Skjold; Zhan, Wei; Aarseth, Bjørn Brevig; Nguyen, Phuong Dan; Johansen, Klaus Magnus H & Vines, Lasse [Vis alle 7 forfattere av denne artikkelen] (2016). Bandgap measurements by STEM-EELS. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Zhan, Wei; Jensen, Ingvild Julie Thue; Granerød, Cecilie Skjold; Venkatachalapathy, Vishnukanthan & Brillson, Leonard J. [Vis alle 8 forfattere av denne artikkelen] (2016). Mapping of Optical band gaps using Electron Energy Loss Spectroscopy in ZnCdO-alloys. Fulltekst i vitenarkiv
• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Alkauskas, A & Svensson, Bengt Gunnar (2016). Polaronic hole binding by the Zn vacancy in ZnO. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Sky, Thomas Neset; Vines, Lasse; Frodason, Ymir Kalmann; Riise, Heine Nygard & Bjørheim, Tor Svendsen [Vis alle 7 forfattere av denne artikkelen] (2016). The dynamic interplay between intrinsic defects and shallow donor dopants (Al and Ga) in ZnO. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Sky, Thomas Neset; Vines, Lasse & Svensson, Bengt Gunnar (2016). Reaction diffusion simulation - a link between Experiment and DFT. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Frodason, Ymir Kalmann; Tuomisto, Filip; Makkonen, Ilja & Vines, Lasse (2016). Formation of Zn- and O-vacancy Clusters in ZnO by thermal treatment. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Sky, Thomas Neset; Vines, Lasse & Svensson, Bengt Gunnar (2015). Defects, Impurities and Diffusion in ZnO. Fulltekst i vitenarkiv
• Zhan, Wei; Venkatachalapathy, Vishnukanthan; Jensen, Ingvild Julie Thue; Granerød, Cecilie Skjold; Flage-Larsen, Espen & Johansen, Klaus Magnus H [Vis alle 9 forfattere av denne artikkelen] (2015). STEM-EELS Band Gap Measurement in Zn1-XCdXO Thin Films. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Sky, Thomas Neset; Vines, Lasse; Frodason, Ymir Kalmann; Riise, Heine Nygard & Bjørheim, Tor Svendsen [Vis alle 7 forfattere av denne artikkelen] (2015). The Interplay between Ga Dopants and Intrinsic Defects in ZnO - Seen from the Diffusion Perspective. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H (2014). Introduction to semiconductors and interfaces. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Sky, Thomas Neset; Herklotz, Frank; Haug, Halvard & Svensson, Bengt Gunnar (2014). IR absorption strength of Ni on Zinc-site in crystalline Zinc Oxid. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Vines, Lasse; Bjørheim, Tor Svendsen; Ramón, Schifano & Svensson, Bengt Gunnar (2014). ZnO as a transparent conductive oxide (TCO) material for solar cells. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Vines, Lasse; Bjørheim, Tor Svendsen; Schifano, Ramon & Svensson, Bengt Gunnar (2014). Aluminium Diffusion in Single Crystalline Zinc Oxide. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Vines, Lasse; Bjørheim, Tor Svendsen; Ramón, Schifano & Svensson, Bengt Gunnar (2013). Aluminium Diffusion and Solubility in Single Crystalline Zinc Oxide. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Knutsen, Knut Erik; Norby, Truls & Svensson, Bengt Gunnar (2013). Defect Configuration and Migration of in-diffused H and Li in single crystalline ZnO. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Bjørheim, Tor Svendsen; Knutsen, Knut Erik; Norby, Truls & Svensson, Bengt Gunnar (2013). Li and H related defects in ZnO. Fulltekst i vitenarkiv
• Bjørheim, Tor Svendsen; Johansen, Klaus Magnus H & Norby, Truls (2013). Defect structure of ZnO from first principles calculations. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H; Vines, Lasse; Monakhov, Edouard & Svensson, Bengt Gunnar (2012). Hydrogen diffusion and implantation induced defect interaction in single crystalline ZnO. Fulltekst i vitenarkiv
• Johansen, Klaus Magnus H (2012). Solenergi. Fulltekst i vitenarkiv
• Knutsen, Knut Erik; Neuvonen, Pekka Tapio; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar & Kuznetsov, Andrej (2011). Trap-limited Li diffusion in melt grown ZnO. 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
• Johansen, Klaus Magnus H (2011). Group one impurities in single crystalline Zinc Oxide. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Zinc Oxide (ZnO) has been used as a material in many different technologies from pharmaceuticals to electronics. This exciting material can also be utilized as a wide band gap semiconductor for application in optoelectronic devices. The availability of Zn, the possibility to grow single crystal bulk material and the exitonic binding energy of 60 meV makes this material especially interesting. Even though the material has been studied already since the late 1920s there are still some fundamental properties of ZnO as a semiconductor which are not yet fully understood e.g. the inherent n-type activity and the challenge of achieving stable p-type doping.<br> The present work is a study of dopants and impurities in ZnO, with a focus on H and Li and their interplay in hydrothermally grown (HT) ZnO. Doping with H typically increases the electron concentration in the material, either by direct donor activity or by passivation of acceptors. Doping by Li on the other hand typically results in material with high resistivity, which is explained by Li contributing both as acceptor and donor on the substitutional Zn-site and interstitial site, respectively. Both elements may therefore significantly contribute to the electrical properties of ZnO.<br> Both H and Li are light elements with small ionic radius, and thus the diffusivity along the interstitial route is expected to be high. In this work H diffusion has been studied by secondary ion mass spectrometry (SIMS). From this the H diffusion in hydrothermally grown material was found to be trap limited with an activation energy of 0.8-0.9 eV and with a dissociation energy from the diffusion trap of approximately 1.5 eV. Since H and Li are known to form a complex together and the concentration of Li is close to the observed trap concentration Li was suggested to be the diffusion trap for H, however contribution from other defects or impurities could not be ruled out. To approach this question from a different angle, Fourier transformed infrared absorption spectroscopy (FTIR) was employed to study the 3577 cm−1 local vibrational mode, previously identified as a OH-Li-complex. The 3577 cm−1 line had been found to survive heat treatments of several hours at 1200◦C, which is inconsistent with the estimated dissociation energy of the H diffusion trap. However, in this thesis it is shown that the reason for the high thermal stability is efficient re-trapping of H (and possibly Li) when the sample is let to cool down slowly to room temperature. In this way the complex responsible for the 3577 cm−1 vibrational mode is reformed and the peak can therefore be observed even after heat treatment at temperatures far above the thermal stability of the complex. Furthermore, by comparing results from both SIMS and FTIR, no correlation between the as-grown 3577 cm−1 peak intensity and the Li-concentration was found, indicating that most of the Li atoms in the as-grown state are not passivated by H. SIMS-measurements also revealed an in-homogeneous distribution of Li repeated in the lateral directions in some of the studied wafers. It is speculated that these in-homogeneities are related to the presence of c-axis inversion domains as observed by transmission electron microscopy (TEM) and it is speculated that they might contribute to the high apparent thermal stability of the 3577 cm−1 vibrational mode.<br> The third angle of approach employed in this thesis is the combination of SIMS and positron annihilation spectroscopy (PAS) together with theoretical estimates. The PAS-technique is very well suited to study open volume defects. One of the main results in this work is the identification of the positron annihilation signature of Li occupying the Zn-site, which showed that most of the Li atoms in as-grown n-type HT-ZnO is in the acceptor-state (substitutional Zn-site). It also showed that in melt grown ZnO doped with 1.5×1019 Li/cm3 more than 2-3×1018 cm−3 of the Li atoms resides on the Zn-site, showing the possibility of obtaining large concentrations of Li on the Zn-site in the acceptor state.<br> The identification of the annihilation signature of LiZn also opened the possibility to study the effect of hydrogenation of HT-ZnO by PAS, where H is shown to efficiently passivate the Liacceptors leaving Zn-vacancies as the dominant positron trap. However, in material where Li had been removed prior to hydrogenation H is found to be trapped by Zn-vacancies.<br> This work shows that there is a strong interplay between H and Li in ZnO. There are strong arguments that Li is the main trapping site for H-diffusion based on the combination of results from techniques like SIMS, FTIR and PAS, however other sites may not be completely excluded and there is also evidence of relatively complicated dynamics related to the behavior of H and Li in ZnO, involving several different sites for H. This work has also confirmed that several properties of hydrothermally grown ZnO may vary from wafer to wafer and using good reference samples are necessary to be able to draw correct conclusions.

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