Augustinas Galeckas

• Azarov, Alexander; Galeckas, Augustinas; Mieszczyński, Cyprian; Hallen, Anders & Kuznetsov, Andrej (2020). Effects of annealing on photoluminescence and defect interplay in ZnO bombarded by heavy ions: Crucial role of the ion dose. Journal of Applied Physics.  ISSN 0021-8979.  127 . doi: 10.1063/1.5134011
• Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Coutinho, José & Vines, Lasse (2020). Influence of hydrogen implantation on emission from the silicon vacancy in 4H-SiC. Journal of Applied Physics.  ISSN 0021-8979.  127 . doi: 10.1063/1.5140659 Fulltekst i vitenarkiv. Vis sammendrag

  The silicon vacancy (VSi) in 4H-SiC is a room temperature single-photon emitter with a controllable high-spin ground state and is a promising candidate for future quantum technologies. However, controlled defect formation remains a challenge, and, recently, it was shown that common formation methods such as proton irradiation may, in fact, lower the intensity of photoluminescence (PL) emission from VSi as compared to other ion species. Herein, we combine hybrid density functional calculations and PL studies of the proton-irradiated n-type 4H-SiC material to explore the energetics and stability of hydrogen-related defects, situated both interstitially and in defect complexes with VSi, and confirm the stability of hydrogen in different interstitial and substitutional configurations. Indeed, VSi-H is energetically favorable if VSi is already present in the material, e.g., following irradiation or ion implantation. We demonstrate that hydrogen has a significant impact on electrical and optical properties of VSi, by altering the charge states suitable for quantum technology applications, and provide an estimate for the shift in thermodynamic transition levels. Furthermore, by correlating the theoretical predictions with PL measurements of 4H-SiC samples irradiated by protons at high (400 C) and room temperatures, we associate the observed quenching of VSi emission in the case of high-temperature and high-fluence proton irradiation with the increased mobility of Hi, which may initiate VSi-H complex formation at temperatures above 400 C. The important implication of hydrogen being present is that it obstructs the formation of reliable and efficient single-photon emitters based on silicon vacancy defects in 4H-SiC.

• 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
• Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Müting, Johanna; Ayedh, Hussein Mohammed Hussein; Grossner, Ulrike; Coutinho, José; Frodason, Ymir Kalmann & Vines, Lasse (2019). Electrical charge state identification and control for the silicon vacancy in 4H-SiC. npj Quantum Information.  ISSN 2056-6387.  5(1), s 1- 9 . doi: 10.1038/s41534-019-0227-y Fulltekst i vitenarkiv.
• Ayedh, Hussein Mohammed Hussein; Grigorev, Aleksei; Galeckas, Augustinas; Svensson, Bengt Gunnar & Monakhov, Eduard (2019). Annealing Kinetics of the Interstitial Carbon–Dioxygen Complex in Silicon. Physica Status Solidi (a) applications and materials science.  ISSN 1862-6300.  216(14), s 1- 5 . doi: 10.1002/pssa.201800986
• 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
• Kjeldstad, Torunn; Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Azarov, Alexander; Monakhov, Eduard & Galeckas, Augustinas (2019). Monitoring selective etching of self-assembled nanostructured a-Si:Al films. Nanotechnology.  ISSN 0957-4484.  30(13), s 1- 5 . doi: 10.1088/1361-6528/aafb86 Fulltekst i vitenarkiv.
• Kjeldstad, Torunn; Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Jensen, Ingvild Julie Thue; Monakhov, Eduard & Galeckas, Augustinas (2019). Surface effects and optical properties of self-assembled nanostructured a-Si:Al. Nanomaterials.  ISSN 2079-4991.  9(8), s 1- 12 . doi: 10.3390/nano9081106 Fulltekst i vitenarkiv. Vis sammendrag

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

• Olsen, Vegard Skiftestad; Baldissera, Gustavo; Zimmermann, Christian; Granerød, Cecilie Skjold; Bazioti, Kalliopi; Galeckas, Augustinas; Svensson, Bengt Gunnar; Kuznetsov, Andrej; Persson, Clas; Prytz, Øystein & Vines, Lasse (2019). Evidence of defect band mechanism responsible for band gap evolution in (ZnO)1−x(GaN)x alloys. Physical review B (PRB).  ISSN 2469-9950.  100(16) . doi: 10.1103/PhysRevB.100.165201 Fulltekst i vitenarkiv.
• Rauwel, P; Galeckas, Augustinas & Rauwel, Erwan (2019). Time evolution of ZnO-CNT photoluminescence under variable ambient and temperature conditions. IOP Conference Series: Materials Science and Engineering.  ISSN 1757-8981.  613(1) . doi: 10.1088/1757-899X/613/1/012031 Fulltekst i vitenarkiv.
• Rauwel, Protima; Galeckas, Augustinas; Ducroquet, Frédérique & Rauwel, Erwan (2019). Selective photocurrent generation in HfO2 and carbon nanotube hybrid nanocomposites under Ultra-Violet and visible photoexcitations. Materials letters (General ed.).  ISSN 0167-577X.  246, s 45- 48 . doi: 10.1016/j.matlet.2019.03.030
• Schifano, Ramon; Jakiela, R; Galeckas, Augustinas; Kopalko, K; Herklotz, Frank; Johansen, Klaus Magnus H & Vines, Lasse (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.
• Ayedh, Hussein Mohammed Hussein; Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Hassan, Jawad U; Bergman, J. P.; Nipoti, Roberta; Hallen, Anders & Svensson, Bengt Gunnar (2018). Controlling the carbon vacancy in 4H-SiC by thermal processing. ECS Transactions.  ISSN 1938-5862.  86(12), s 91- 97 . doi: 10.1149/08612.0091ecst
• Bergum, Kristin; Riise, Heine Nygard; Gorantla, Sandeep Madhukar; Lindberg, Per; Jensen, Ingvild Julie Thue; Gunnæs, Anette Eleonora; Galeckas, Augustinas; Diplas, Spyridon; Svensson, Bengt Gunnar & Monakhov, Edouard (2018). Improving carrier transport in Cu2O thin films by rapid thermal annealing. Journal of Physics: Condensed Matter.  ISSN 0953-8984.  30(7) . doi: 10.1088/1361-648X/aaa5f4
• Galeckas, Augustinas; Almeida Carvalho, Patricia; Ma, Quanbao; Azarov, Alexander; Hovden, Sigurd Slettemark; Thøgersen, Annett; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2018). Optical and microstructural investigation of heavy B-doping effects in sublimation-grown 3C-SiC. Materials Science Forum.  ISSN 0255-5476.  924, s 221- 224 . doi: 10.4028/www.scientific.net/MSF.924.221 Vis sammendrag

  In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000°C have been cross-correlated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects.

• 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.
• Montero, José; Galeckas, Augustinas & Karazhanov, Smagul (2018). Photoluminescence Properties of Photochromic Yttrium Hydride Films Containing Oxygen. Physica status solidi. B, Basic research.  ISSN 0370-1972.  255(8) . doi: 10.1002/pssb.201800139 Fulltekst i vitenarkiv.
• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas; Azarov, Alexander; Vines, Lasse & Kuznetsov, Andrej (2018). Phase stability and strain accumulation in CdO as a function of Cd/O supply during MOVPE synthesis. Superlattices and Microstructures.  ISSN 0749-6036.  120, s 569- 577 . doi: 10.1016/j.spmi.2018.06.017
• Azarov, Alexander; Galeckas, Augustinas; Wendler, Elke; Ellingsen, Josef Gert Åsheim; Monakhov, Edouard & Svensson, Bengt Gunnar (2017). Normal and reverse defect annealing in ion implanted II-VI oxide semiconductors. Journal of Applied Physics.  ISSN 0021-8979.  122, s 115701 . doi: 10.1063/1.4997847
• Galeckas, Augustinas; Ayedh, Hussein Mohammed Hussein; Bergman, J. Peder & Svensson, Bengt Gunnar (2017). Depth-resolved Carrier Lifetime Measurements in 4H-SiC Epilayers Monitoring Carbon Vacancy Elimination. Materials Science Forum.  ISSN 0255-5476.  897, s 258- 261 . doi: 10.4028/www.scientific.net/MSF.897.258
• Kjeldstad, Torunn; Thøgersen, Annett; Nilsen, Ola; Monakhov, Edouard & Galeckas, Augustinas (2017). Controllable template approach for ZnO nanowire growth. Physica Status Solidi (a) applications and materials science.  ISSN 1862-6300.  214(2), s 1- 6 . doi: 10.1002/pssa.201600480 Vis sammendrag

  Anodic aluminum oxide (AAO) is an optically transparent material with uniform hexagonal pores, which has widely been used as a template for nanowire growth. This study examines the potential of utilizing commercially available AAO to fabricate sub-10 nm ZnO nanowires by atomic layer deposition. The pore diameter of the AAO framework is reduced by controlled deposition of . Subsequently, ZnO is deposited and ZnO nanowires are obtained. The analysis of structural and optical properties shows that the nanowires are polycrystalline, and exhibit a pronounced near band edge emission. Photoluminescence (PL) measurements are performed to monitor the effect of additional coating with and ZnO, on the optical stability of the AAO. The measurements indicate that the PL is highly influenced by the adsorption and desorption of species from the ambient at the surface. ALD deposition of a thin layer reduces considerably the effect of ambient atmosphere. The layer of facilitates PL characterization of very thin ZnO nanowires.

• Ma, Quanbao; Carvalho, Patricia; Galeckas, Augustinas; Azarov, Alexander; Hovden, Sigurd Slettemark; Thøgersen, Annett; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2017). Characterization of B-implanted 3C-SiC for intermediate band solar cells. Materials Science Forum.  ISSN 0255-5476.  897, s 299- 302 . doi: 10.4028/www.scientific.net/MSF.897.299 Vis sammendrag

  Sublimation-grown 3C-SiC crystals were implanted with B ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 1.3×1017 atoms/cm2 in order to form intermediate band (IB) in 3C-SiC. The samples were then annealed at 1400 °C for 60 min. An anomalous area in the center was observed in the PL emission pattern. The SIMS analysis indicated that the B concentration was the same both within and outside the anomalous area. The buried boron box-like concentration profile can reach ~3×1021 cm-3 in the plateau region. In the anomalous area a broad emission band (possible IB) emerges at around ~1.7-1.8 eV, which may be associated with B-precipitates having a sufficiently high density. Sublimation-grown 3C-SiC crystals were implanted with B ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 1.3×1017 atoms/cm2 in order to form intermediate band (IB) in 3C-SiC. The samples were then annealed at 1400 °C for 60 min. An anomalous area in the center was observed in the PL emission pattern. The SIMS analysis indicated that the B concentration was the same both within and outside the anomalous area. The buried boron box-like concentration profile can reach ~3×1021 cm-3 in the plateau region. In the anomalous area a broad emission band (possible IB) emerges at around ~1.7-1.8 eV, which may be associated with B-precipitates having a sufficiently high density.

• Rauwel, Erwan; Galeckas, Augustinas; Soares, M Rosario & Rauwel, Protima (2017). Influence of the Interface on the Photoluminescence Properties in ZnO Carbon-Based Nanohybrids. Journal of Physical Chemistry C.  ISSN 1932-7447.  121(27), s 14879- 14887 . doi: 10.1021/acs.jpcc.7b03070
• Rauwel, Protima; Galeckas, Augustinas; Salumaa, Martin; Aasna, Andres; Ducroquet, Frédérique & Rauwel, Erwan Yann (2017). Investigations on new carbon-based nanohybrids combining carbon nanotubes, HfO2 and ZnO nanoparticles. IOP Conference Series: Materials Science and Engineering.  ISSN 1757-8981.  175(1) . doi: 10.1088/1757-899X/175/1/012064
• Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Mei, Zengxia; Liu, Lishu; Du, Xiaolong; Galeckas, Augustinas; Monakhov, Edouard; Svensson, Bengt Gunnar & Kuznetsov, Andrej (2016). Self-diffusion measurements in isotopic heterostructures of undoped and in situ doped ZnO: Zinc vacancy energetics. Physical Review B. Condensed Matter and Materials Physics.  ISSN 1098-0121.  94, s 195208 . doi: 10.1103/PhysRevB.94.195208
• 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, Basic research.  ISSN 0370-1972.  253(2), s 273- 278 . doi: 10.1002/pssb.201552441
• Ma, Quanbao; Galeckas, Augustinas; Azarov, Alexander; Thøgersen, Annett; Carvalho, Patricia; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Liu, Xinyu; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2016). Boron-implanted 3C-SiC for intermediate band solar cells. Materials Science Forum.  ISSN 0255-5476.  858, s 291- 294 . doi: 10.4028/www.scientific.net/MSF.858.291 Fulltekst i vitenarkiv. Vis sammendrag

  Sublimation-grown 3C-SiC crystals were implanted with 2 atomic percent of boron ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 8.5×1016 atoms/cm2. The samples were then annealed at 1400, 1500 and 1600 °C for 1h at each temperature. The buried boron box-like concentration profile can reach ~2×1021 cm-3 in the plateau region. The optical activity of the incorporated boron atoms was deduced from the evolution in absorption and emission spectra, indicating possible pathway for achieving an intermediate band behavior in boron doped 3C-SiC at sufficiently high dopant concentrations.

• Rauwel, Erwan Yann; Galeckas, Augustinas; Rauwel, Protima; Hansen, Per-Anders; Wragg, David; Nilsen, Ola & Fjellvåg, Helmer (2016). Metal oxide nanoparticles embedded in rare-earth matrix for low temperature thermal imaging applications. Materials Research Express.  ISSN 2053-1591.  3(5) . doi: 10.1088/2053-1591/3/5/055010
• Rauwel, Protima; Galeckas, Augustinas; Salumaa, Martin; Ducroquet, Frédérique & Rauwel, Erwan (2016). Photocurrent generation in carbon nanotube/cubic-phase HfO2 nanoparticle hybrid nanocomposites. Beilstein Journal of Nanotechnology.  ISSN 2190-4286.  7, s 1075- 1085 . doi: 10.3762/bjnano.7.101
• Rauwel, Protima; Salumaa, Martin; Aasna, Andres; Galeckas, Augustinas & Rauwel, Erwan Yann (2016). A review of the synthesis and photoluminescence properties of hybrid ZnO and carbon nanomaterials. Journal of Nanomaterials.  ISSN 1687-4110.  2016:5320625, s 1- 12 . doi: 10.1155/2016/5320625
• Riise, Heine Nygard; Olsen, Vegard Skiftestad; Azarov, Alexander; Galeckas, Augustinas; Sky, Thomas Neset; Svensson, Bengt Gunnar & Monakhov, Edouard (2016). Local homoepitaxy of zinc oxide thin films by magnetron sputtering. Thin Solid Films.  ISSN 0040-6090.  601, s 18- 21 . doi: 10.1016/j.tsf.2015.09.043
• Schrade, Matthias; Magraso, Anna; Galeckas, Augustinas; Finstad, Terje & Norby, Truls (2016). The Band Gap of BaPrO3 Studied by Optical and Electrical Methods. Journal of The American Ceramic Society.  ISSN 0002-7820.  99(2), s 492- 498 . doi: 10.1111/jace.13961
• Syväjärvi, Mikael; Ma, Quanbao; Jokubavicius, Valdas; Galeckas, Augustinas; Sun, Jianwu; Liu, Xinyu; Jansson, Mattias; Wellmann, Peter; Linnarsson, Margareta; Runde, Paal; Johansen, Bertil; Thøgersen, Annett; Diplas, Spyridon; Carvalho, Patricia; Løvvik, Ole Martin; Wright, Daniel Nilsen; Azarov, Alexander & Svensson, Bengt Gunnar (2016). Cubic silicon carbide as a potential photovoltaic material. Solar Energy Materials and Solar Cells.  ISSN 0927-0248.  145, s 104- 108 . doi: 10.1016/j.solmat.2015.08.029 Fulltekst i vitenarkiv. Vis sammendrag

  In this work we present a significant advancement in cubic silicon carbide (3C-SiC) growth in terms of crystal quality and domain size, and indicate its potential use in photovoltaics. To date, the use of 3C-SiC for photovoltaics has not been considered due to the band gap of 2.3 eV being too large for conventional solar cells. Doping of 3C-SiC with boron introduces an energy level of 0.7 eV above the valence band. Such energy level may form an intermediate band (IB) in the band gap. This IB concept has been presented in the literature to act as an energy ladder that allows absorption of sub-bandgap photons to generate extra electron–hole pairs and increase the efficiency of a solar cell. The main challenge with this concept is to find a materials system that could realize such efficient photovoltaic behavior. The 3C-SiC bandgap and boron energy level fits nicely into the concept, but has not been explored for an IB behavior. For a long time crystalline 3C-SiC has been challenging to grow due to its metastable nature. The material mainly consists of a large number of small domains if the 3C polytype is maintained. In our work a crystal growth process was realized by a new approach that is a combination of initial nucleation and step-flow growth. In the process, the domains that form initially extend laterally to make larger 3C-SiC domains, thus leading to a pronounced improvement in crystalline quality of 3C-SiC. In order to explore the feasibility of IB in 3C-SiC using boron, we have explored two routes of introducing boron impurities; ion implantation on un-doped samples and epitaxial growth on un-doped samples using pre-doped source material. The results show that 3C-SiC doped with boron is an optically active material, and thus is interesting to be further studied for IB behavior. For the ion implanted samples the crystal quality was maintained even after high implantation doses and subsequent annealing. The same was true for the samples grown with pre-doped source material, even with a high concentration of boron impurities. We present optical emission and absorption properties of as-grown and boron implanted 3C-SiC. The low-temperature photoluminescence spectra indicate the formation of optically active deep boron centers, which may be utilized for achieving an IB behavior at sufficiently high dopant concentrations. We also discuss the potential of boron doped 3C-SiC base material in a broader range of applications, such as in photovoltaics, biomarkers and hydrogen generation by splitting water

• Azarov, Alexander; Galeckas, Augustinas; Hallen, Anders; Kuznetsov, Andrej; Monakhov, Edouard & Svensson, Bengt Gunnar (2015). Optical activity and defect/dopant evolution in ZnO implanted with Er. Journal of Applied Physics.  ISSN 0021-8979.  118, s 125703 . doi: 10.1063/1.4931423
• Raeissi, Bahman; Ganagona, Naveengoud; Galeckas, Augustinas; Monakhov, Edouard & Svensson, Bengt Gunnar (2014). PL and DLTS analysis of carbon–related centers in irradiated p–type Cz–Si. Solid State Phenomena.  ISSN 1012-0394.  205-206, s 224- 227 . doi: 10.4028/www.scientific.net/SSP.205-206.224
• Iwu, Kingsley Odinaka; Galeckas, Augustinas; Diplas, Spyridon; Seland, Frode; Kuznetsov, Andrej & Norby, Truls (2014). Effects of temperature, triazole and hot-pressing on the performance of TiO2 photoanode in a solid-state photoelectrochemical cell. Electrochimica Acta.  ISSN 0013-4686.  115, s 66- 74 . doi: 10.1016/j.electacta.2013.10.095 Vis sammendrag

  The photocurrent of hydrogen generating solid-state photoelectrochemical cell utilising a polybenzimidazole proton-conducting membrane and gaseous anode reactants has been enhanced by operation at higher temperatures. With a bias of 0 V for example, photocurrent increased from 15 to 30 μA/cm2 on moving from 25 °C to 45 °C. The increase in photocurrent, which was limited by the dehydration of the cell, was shown to have contribution from improved electrode kinetics. Modification of TiO2 surface with triazole, a conjugated heterocyclic compound, led to significant increase in photocurrent up to 4 fold increase at 0 V and 25 °C. This was attributed to improved separation of photogenerated charge carriers, as confirmed by correspondingly increased carrier lifetimes from 50 ns to 90 ns for triazole-modified TiO2. Assembly of the photoelectrochemical cell by hot-pressing induced a ̴ 0.3 eV red shift in optical absorption edge of TiO2, in agreement with a shift of its valence band maximum to higher binding energy.

• Mayandi, Jeyanthinath; Finstad, Terje; Foss, Steinar; Galeckas, Augustinas & Stange, Marit Synnøve Sæverud (2014). A comparative study of 1.5 μm photoluminescence from (Er, Si) and (Er, Ge) co-sputtered with Al2O3 on Si. Journal of Alloys and Compounds.  ISSN 0925-8388.  590, s 5- 8 . doi: 10.1016/j.jallcom.2013.12.060 Vis sammendrag

  We present a comparative study of the 1.54lm photoluminescence (PL) from Al2O3:(Er, Si) and Al2O3:(Er, Ge) films co-sputtered on Si substrates using a composite target. The PL yield of Si- and Ge- doped films subjected to different thermal treatment in the range 500–1100 °C is referenced against that of a control Al2O3:(Er) structure. The Er-related emission reaches maximum upon annealing at 700 °C for the Al2O3:(Er, Si) and 500 °C for the Al2O3:(Er, Ge) films, in both cases decreasing at higher annealing tem- peratures. Ge co-doped films are found to be approximately 20 times less luminous than the reference Al2O3:(Er) structure, whereas Si co-doping leads to greatly enhanced emission at 1.54 lm. By adapting energy filtered transmission electron microscopy (EFTEM), the presence of ����2 nm Si nanoclusters was revealed, whereas no indications of Ge clusters or crystals could be observed implying that mere presence of Ge in the Al2O3 matrix can dramatically reduce the luminescence efficiency. We discuss the possible reasons for not forming the Ge nanoclusters in the Al2O3 host and the apparent quenching of the Er- related emission.

• Rauwel, Protima; Galeckas, Augustinas & Rauwel, Erwan Yann (2014). One step synthesis of pure cubic and monoclinic HfO<inf>2</inf> nanoparticles: Effects of temperature and ambient on the photoluminescent properties. ECS Transactions.  ISSN 1938-5862.  64(44), s 19- 28 . doi: 10.1149/06444.0019ecst
• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas & Kuznetsov, Andrej (2014). Tunneling in ZnO/ZnCdO quantum wells towards next generation photovoltaic cells. Solar Energy.  ISSN 0038-092X.  106, s 82- 87 . doi: 10.1016/j.solener.2013.11.032
• Iwu, Kingsley Odinaka; Galeckas, Augustinas; Kuznetsov, Andrej & Norby, Truls (2013). Solid-state photoelectrochemical H2 generation with gaseous reactants. Electrochimica Acta.  ISSN 0013-4686.  97, s 320- 325 . doi: 10.1016/j.electacta.2013.03.013
• Li, Jun-Qiang; Mei, Zeng-Xia; Ye, Da-Qian; Liang, Huili; Liu, Lishu; Liu, Yaoping; Galeckas, Augustinas; Kuznetsov, Andrej & Du, Xiaolong (2013). Engineering of optically defect free Cu2O enabling exciton luminescence at room temperature. Optical Materials Express.  ISSN 2159-3930.  3(12), s 2072- 2077 . doi: 10.1364/OME.3.002072
• Long, Ethan Schuyler; Galeckas, Augustinas; Kuznetsov, Andrej; Ronda, Antoine; Favre, Luc; Berbezier, Isabelle & Radamson, Henry H. (2013). Nano-structuring in SiGe by oxidation induced anisotropic Ge self-organization. Journal of Applied Physics.  ISSN 0021-8979.  113(10) . doi: 10.1063/1.4794991 Fulltekst i vitenarkiv.
• Lund, Esben; Galeckas, Augustinas; Azarov, Alexander; Monakhov, Edouard & Svensson, Bengt Gunnar (2013). Photoluminescence of reactively sputtered Ag2O films. Thin Solid Films.  ISSN 0040-6090.  536, s 156- 159 . doi: 10.1016/j.tsf.2013.04.026
• Lund, Esben; Galeckas, Augustinas; Monakhov, Edouard & Svensson, Bengt Gunnar (2013). Basic optical and electronic properties of Ag2Cu2O3 crystalline films. Thin Solid Films.  ISSN 0040-6090.  531, s 185- 188 . doi: 10.1016/j.tsf.2013.01.044
• Sellappan, Raja; Sun, Jie; Galeckas, Augustinas; Lindvall, Niclas; Yurgens, August; Kuznetsov, Andrej & Chakarov, Dinko (2013). Influence of graphene synthesizing techniques on the photocatalytic performance of graphene-TiO2 nanocomposites. Physical Chemistry, Chemical Physics - PCCP.  ISSN 1463-9076.  15(37), s 15528- 15537 . doi: 10.1039/c3cp52457d
• Trunk, Mareike; Galeckas, Augustinas; Venkatachalapathy, Vishnukanthan; Azarov, Alexander & Kuznetsov, Andrej (2013). Carrier dynamics in linearly and step graded bandgap Zn1-xCdxO structures. Applied Physics Letters.  ISSN 0003-6951.  102(19) . doi: 10.1063/1.4807387
• Iwu, Kingsley Odinaka; Galeckas, Augustinas; Rauwel, Protima; Kuznetsov, Andrej & Norby, Truls (2012). One-dimensional WO3 and its hydrate: One-step synthesis, structural and spectroscopic characterization. Journal of Solid State Chemistry.  ISSN 0022-4596.  185, s 245- 252 . doi: 10.1016/j.jssc.2011.11.001
• Knutsen, Knut Erik; Galeckas, Augustinas; Zubiaga, Asier; Tuomisto, Filip; Farlow, Gary C.; Svensson, Bengt Gunnar & Kuznetsov, Andrej (2012). Zinc vacancy and oxygen interstitial in ZnO revealed by sequential annealing and electron irradiation. Physical Review B. Condensed Matter and Materials Physics.  ISSN 1098-0121.  86(12) . doi: 10.1103/PhysRevB.86.121203 Fulltekst i vitenarkiv.
• Long, Ethan Schuyler; Azarov, Alexander; Kløw, Frode; Galeckas, Augustinas; Kuznetsov, Andrej & Diplas, Spyridon (2012). Ge redistribution in SiO2/SiGe structures under thermal oxidation: Dynamics and predictions. Journal of Applied Physics.  ISSN 0021-8979.  111(2) . doi: 10.1063/1.3677987 Fulltekst i vitenarkiv. Vis sammendrag

  Several fundamental aspects of the oxidation-induced redistribution of Ge in thin films of SiGe are studied. This includes the incorporation of Ge into the oxide and the formation of what is alternatively referred to as pile-up, snow-plow, or a germanium-rich layer. Experimental data from the present work shows longer oxidation times leading to an increase of Ge content in the pile-up region and eventually creating a single high Ge content pile-up layer by entirely consuming the initial SiGe layer. The pile-up effect was shown to occur at the oxidation interface, with the highest Ge content occurring at the same interface. For a given oxide thickness, the redistribution of Ge and the formation of a pile-up region was shown experimentally to be independent of temperature in the range between 800 °C and 1000 °C. Simulations using common models for the oxidation of Si and diffusion of Si in SiGe indicate that temperature does have an influence on the composition of the pile-up layer, though the range of achievable compositions is limited. The flux of Si due to diffusion of Si in SiGe relative to the oxidation-induced flux of Si out of the SiGe is integral to the formation and dimensions of a pile-up region. Two predictive relations were derived for describing the dynamics of oxidation of SiGe. The first relation is given for determining the pile-up layer thickness as a function of oxide thickness and the composition of the pile-up layer. The second relation assumes a limited supply of Si and is for determination of the minimum initial thickness of a SiGe layer to avoid oxidation of Ge. The validity of these equations was confirmed experimentally by RBS and XPS data from the present work. The proposed models may be used in nanostructuring of thin films of SiGe by oxidation and in the design of core-shell structures and transistors. This is all done with a focus on oxidation of epitaxial thin films (< 100 nm) of Si1-XGeX in dry O2 at 1 atm between 800 °C and 1000 °C.

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• Azarov, Alexander; Galeckas, Augustinas; Mieszczyński, Cyprian; Hallen, Anders & Kuznetsov, Andrej (2019). Effects of annealing on photoluminescence and defect interplay in ZnO bombarded with heavy ions: crucial role of the ion dose.
• Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Müting, Johanna; Ayedh, Hussein Mohammed Hussein; Grossner, Ulrike; Coutinho, J & Vines, Lasse (2019). Electrical enhancement and switching of single-photon emission from the silicon vacancy in 4H-SiC.
• Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Müting, Johanna; Ayedh, Hussein Mohammed Hussein; Grossner, Ulrike; Coutinho, José; Frodason, Ymir Kalmann & Vines, Lasse (2019). Electrical charge-state identification and emission intensity modulation of the silicon vacancy in 4H-SiC.
• Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Müting, Johanna; Ayedh, Hussein Mohammed Hussein; Grossner, Ulrike; Coutinho, José & Vines, Lasse (2019). Electrical enhancement and switching of single-photon emission from the silicon vacancy in 4H-Si. Vis sammendrag

  The high-spin ground state and bright single-photon emission of the silicon vacancy (VSi) in 4H-SiC offer exciting possibilities for quantum technology and spintronics applications, especially as both are available at room temperature [1,2]. However, quantum compatibility only exists for the singly negative VSi, and single-photon counts are still too low to realize efficient spin-photon interfaces without resorting to complex nanofabrication methods [3]. Herein, we demonstrate enhanced optical emission from VSi using Schottky barrier diode (SBD) formation, and attribute our findings to increased occupancies of VSi-1.

• Frodason, Ymir Kalmann; Johansen, Klaus Magnus H; Galeckas, Augustinas & Vines, Lasse (2019). Optical properties of donor-complexed Li_Zn in ZnO.
• Vasquez, Geraldo Cristian; Bazioti, Kalliopi; Galeckas, Augustinas; Johansen, Klaus Magnus H; Granerød, Cecilie Skjold; Nguyen, Phuong Dan; Prytz, Øystein & Vines, Lasse (2019). Luminescent properties of Zn2GeO4 nanoparticles embedded in ZnO.
• 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.
• Ayedh, Hussein Mohammed Hussein; Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Ul Hassan, Jawad; Bergman, J. P.; Nipoti, Roberta; Hallén, Anders & Svensson, Bengt Gunnar (2018). Controlling the Carbon Vacancy in 4H-SiC By Thermal Processing.
• Bathen, Marianne Etzelmüller; Galeckas, Augustinas; Frodason, Ymir Kalmann; Vines, Lasse & Svensson, Bengt Gunnar (2018). Tuning silicon vacancy formation in 4H-SiC via proton irradiation for quantum technology.
• Bathen, Marianne Etzelmüller; Vines, Lasse; Galeckas, Augustinas; Frodason, Ymir Kalmann & Svensson, Bengt Gunnar (2018). Charge state transitions of the silicon vacancy in 4H-SiC: Combined DLTS, PL and DFT study.
• Bathen, Marianne Etzelmüller; Vines, Lasse; Galeckas, Augustinas; Frodason, Ymir Kalmann & Svensson, Bengt Gunnar (2018). Correlating charge state transitions of the Si vacancy to the S1/S2 peaks in DLTS spectra of n-type 4H-SiC.
• Kjeldstad, Torunn; Thøgersen, Annett; Galeckas, Augustinas; Monakhov, Eduard; Stange, Marit Synnøve Sæverud & Nilsen, Ola (2018). Aluminum nanowires in amorphous silicon.
• Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Galeckas, Augustinas; Nilsen, Ola & Monakhov, Eduard (2018). Aluminum nanowires in amorphous silicon.
• 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.
• Venkatachalapathy, Vishnukanthan; Vajeeston, Ponniah; Galeckas, Augustinas; Vines, Lasse & Kuznetsov, Andrej (2018). Direct and indirect bandgaps of Cadmium Oxide.
• Ayedh, Hussein Mohammed Hussein; Azarov, Alexander; Galeckas, Augustinas; Svensson, Bengt Gunnar & Monakhov, Edouard (2017). DLTS study of the interstitial carbon–oxygen complex in proton irradiated p-type Si.
• Bergum, Kristin; Borgersen, Jon Arthur; Ellingsen, Josef Gert Åsheim; Frodason, Ymir Kalmann; Galeckas, Augustinas; Ingebrigtsen, Mads Eide; Kuznetsov, Andrej & Sky, Thomas Neset (2017). Omvisning MiNaLab.
• Frodason, Ymir Kalmann; Bergum, Kristin; Sky, Thomas Neset; Ingebrigtsen, Mads Eide; Borgersen, Jon; Ellingsen, Josef Gert Åsheim; Galeckas, Augustinas & Kuznetsov, Andrej (2017). MiNa-Lab tour highlighting LENS activities.
• 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.
• 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.
• Kjeldstad, Torunn; Galeckas, Augustinas; Nilsen, Ola; Azarov, Alexander; Stange, Marit Synnøve Sæverud; Diplas, Spyridon & Thøgersen, Annett (2017). Self-assembly of Al-nanowires in silicon.
• Kjeldstad, Torunn; Thøgersen, Annett; Monakhov, Edouard & Galeckas, Augustinas (2017). Aluminium nanoparticles embedded in mesoporous aSi:H.
• Kjeldstad, Torunn; Thøgersen, Annett; Monakhov, Edouard & Galeckas, Augustinas (2017). Investigation of mesoporous aSi:H with embedded aluminium nanoparticles.
• Kjeldstad, Torunn; Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Galeckas, Augustinas & Monakhov, Edouard (2017). Self-assembled aluminium nanowires in silicon.
• Nyborg, Martin; Lindberg, Per; Svensson, Bengt Gunnar; Monakhov, Edouard & Galeckas, Augustinas (2017). DC Magnetron Sputter Deposition of CuxO Thin Films The Effect of Target Power and O2 Flow. Vis sammendrag

  In this study, we report on the effect of target power and O2 flow on DC magnetron sputter deposited CuxO thin films. Target power (Ptar) and oxygen flow (QO2) have been varied in the 80 - 100 W and 12-19 sccm range while keeping all other parameters constant.

• Thøgersen, Annett; Kjeldstad, Torunn; Jensen, Ingvild Julie Thue; Muntingh, Agnar Georg Peder; Stange, Marit Synnøve Sæverud; Ulyashin, Alexander; Galeckas, Augustinas; Nilsen, Ola & Monakhov, Edouard (2017). Plasmonic properties of aluminium nanowires in amorphous silicon and inverted silicon nanowires.
• Thøgersen, Annett; Kjeldstad, Torunn; Jensen, Ingvild Julie Thue; Stange, Marit Synnøve Sæverud; Ulyashin, Alexander; Galeckas, Augustinas; Nilsen, Ola; Monakhov, Edouard & Diplas, Spyridon (2017). Growing and characterizing self-organizing aluminium nanowires in amorphous silicon.
• Ayedh, Hussein Mohammed Hussein; Galeckas, Augustinas; Ma, Quanbao; Bobal, Viktor; Iwamoto, Naoya; Nipoti, R; Hallen, Anders & Svensson, Bengt Gunnar (2016). Point defects in 4H-SiC.
• Azarov, Alexander; Galeckas, Augustinas; Hallen, Anders; Monakhov, Edouard & Svensson, Bengt Gunnar (2016). Annealing of Er-implanted ZnO: formation/stability of optically active centers, defect evolution and Li behavior.
• Kjeldstad, Torunn; Galeckas, Augustinas; Monakhov, Edouard; Nilsen, Ola & Thøgersen, Annett (2016). Controllable template approach for ZnO nanowire growth.
• Kjeldstad, Torunn; Galeckas, Augustinas; Nilsen, Ola; Azarov, Alexander; Stange, Marit Synnøve Sæverud; Diplas, Spyridon & Thøgersen, Annett (2016). A new silicon nanostructure.
• Ma, Quanbao; Carvalho, Patricia; Galeckas, Augustinas; Azarov, Alexander; Hovden, Sigurd; Thøgersen, Annett; Wright, Daniel Nilsen; Diplas, Spyridon; Løvvik, Ole Martin; Jokubavicius, Valdas; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2016). Characterization of B-implanted 3C-SiC for intermediate band solar cells.
• Venkatachalapathy, Vishnukanthan; Bakke, Marius Mordal; Galeckas, Augustinas; Vines, Lasse & Kuznetsov, Andrej (2016). Investigation of polar and non-polar Zn(Mg,Cd)O-based Multiple Quantum Wells.
• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas; Azarov, Alexander & Kuznetsov, Andrej (2016). Structural and optical properties of cubic Cd1-xZnxO.
• Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Mei, Zengxia; Liu, Lishu; Du, Xiaolong; Galeckas, Augustinas & Kuznetsov, Andrej (2015). Zinc vacancy energetics revealed by self-diffusion in isotopic ZnO heterostructures.
• Karazhanov, Smagul; Mongstad, TT; Martinsen, Fredrik Aleksander; Amenedo, J. M.; Zayim, E. O.; Mohseni, A.; You, C; Mæhlen, Jan Petter; Galeckas, Augustinas; Moldarev, D; Molff, M; Pishtshev, Aleksandr; Hauback, Bjørn; Subrahmanyam, A & Marstein, Erik Stensrud (2015). Photochromic Materials & Applications.
• Ma, Quanbao; Galeckas, Augustinas; Azarov, Alexander; Thøgersen, Annett; Carvalho, Patricia; Wright, Daniel Nilsen; Diplas, Spyros; Løvvik, Ole Martin; Jokubavicius, Valdas; Liu, Xinyu; Sun, Jianwu; Syväjärvi, Mikael & Svensson, Bengt Gunnar (2015). Boron‐implanted 3C‐SiC for intermediate band solar cells.
• Riise, Heine Nygard; Olsen, Vegard S.; Azarov, Alexander; Galeckas, Augustinas; Monakhov, Edouard & Svensson, Bengt Gunnar (2015). Structural Characteristics of Homoepitaxial Radio Frequency Magnetron Sputter Deposited Zinc Oxide Thin Films.
• Zhan, Wei; Venkatachalapathy, Vishnukanthan; Jensen, Ingvild Julie Thue; Granerød, Cecilie Skjold; Flage-Larsen, Espen; Johansen, Klaus Magnus H; Galeckas, Augustinas; Kuznetsov, Andrej & Prytz, Øystein (2015). STEM-EELS Band Gap Measurement in Zn1-XCdXO Thin Films.
• Riise, Heine Nygard; Schifano, Ramon; Galeckas, Augustinas; Azarov, Alexander; Monakhov, Edouard & Svensson, Bengt Gunnar (2014). A comparative study of annealing effects on Si and Al doped ZnO.
• Venkatachalapathy, Vishnukanthan; Azarov, Alexander; Galeckas, Augustinas & Kuznetsov, Andrej (2014). Synthesis and Characterization of Highly Conductive and Optically Transparent Al-Doped Zn1-xMgxO Films.
• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas; Azarov, Alexander & Kuznetsov, Andrej (2014). Investigation of Ga-Doping Effects in ZnO.
• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas & Kuznetsov, Andrej (2014). Interplay of Structural and Optical properties in CdO.
• Iwu, Kingsley Odinaka; Norby, Truls; Galeckas, Augustinas & Kuznetsov, Andrej (2013). Photoelectrochemical water splitting using an all-solid-state cell with gaseous reactants. Vis sammendrag

  A solid-state proton conducting polymer-ceramic composite was used as electrolyte in a photoelectrochemical (PEC) cell. It was equipped with composite photoanode nanostructures of semiconducting oxides with suitable band gaps, carbon nanoparticles, carbon paper, and polymer electrolyte. The photoanode reactants were gaseous methanol and water vapour. Upon irradiation with UV rich light the all-solid-state and gaseous cell generated considerable photovoltages at open circuit as well as loaded or driven photocurrents. The results and functioning of the cell are interpreted in light of the syntheses, chemistry, nanostructures, and optical properties of the oxides employed, and the concept of all-solid-state PEC solar hydrogen is discussed.

• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas & Kuznetsov, Andrej (2013). Band gap engineering in ZnO for Solar energy harvesting - Multiple Quantum Well Solar Cells.
• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas & Kuznetsov, Andrej (2013). CdO-ZnO Multiple Quantum Wells as Components for Next Generation Solar Cells.
• Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas & Kuznetsov, Andrej (2013). Strained ZnCdO/ZnO multiple quantum well structures.
• Trunk, Mareike; Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas & Kuznetsov, Andrej (2012). Charge carrier dynamics in linearly graded bandgap Zn1-xCdxO structures.
• Iwu, Kingsley Odinaka; Galeckas, Augustinas; Kuznetsov, Andrej & Norby, Truls (2012). A solid state photoelectrochemical cell with gaseous water and methanol as reactants.
• Iwu, Kingsley Odinaka; Galeckas, Augustinas; Kuznetsov, Andrej & Norby, Truls (2012). A solid state photoelectrochemical water splitting cell with a composite Nafion membrane and gaseous reactants.
• Knutsen, Knut Erik; Galeckas, Augustinas; Tuomisto, Filip; Liu, Y. P.; Du, Xiaolong; Svensson, Bengt Gunnar & Kuznetsov, Andrej (2012). Crystallinity and vacancy clustering in Na-doped ZnMgO.

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