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© 2014 American Chemical Society. The authors thank Irina Snigireva and Armando Vicente Solé for their assistance with the SEM measurements and data processing using PyMca, respectively. We thank Peter Cloetens and Sylvain Labouréfor their help and the ESRF for the beam time allocated. This work has been partially supported by the NANOWIRING Marie Curie ITN (EU project no. PITN-GA- 2010 -265073) and by MINECO (Projects MAT 2012-31959 and Consolider Ingenio CSD 2009-00013)., Crossed nanowire structures are the basis for high-density integration of a variety of nanodevices. Owing to the critical role of nanowires intersections in creating hybrid architectures, it has become a challenge to investigate the local structure in crossing points in metal oxide nanowires. Thus, if intentionally grown crossed nanowires are well-patterned, an ideal model to the role of impurities in the coupling formation, structural modifications, and atomic site configuration based on crossed Ga_2O_3/SnO_2 nanowires. Our experiment opens new avenues for further local structure studies with both nanometer resolution and elemental sensitivity., Unión Europea. FP7, Marie Curie ITN (EU), Ministerio de Economía y Competitividad (MINECO), Consolider Ingenio, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2013 American Chemical Society. This work has been supported by MICINN through Projects MAT 2009-07882 and Consolider Ingenio CSD 2009-00013. The authors are grateful to Dr. Luca Gregoratti at the Sincrotrone Elettra Trieste for useful advice on XPS measurements., Elongated micro- and nanostructures of Sn doped or Sn and Cr codoped monoclinic gallium oxide have been grown by a thermal method. The presence of Sn during growth has been shown to strongly influence the morphology of the resulting structures, including Sn doped branched wires, whips, and needles. Subsequent codoping with Cr is achieved through thermal diffusion for photonic purposes. The formation mechanism of the branched structures has been studied by transmission electron microscopy (TEM). Epitaxial growth has been demonstrated in some cases, revealed by a very high quality interface between the central rod and the branches of the structures, while in other cases, formation of extended defects such as twins has been observed in the interface region. The influence of dopants on the energy levels of Ga and O within the structures has been studied by XPS. Micro-Raman spectroscopy was used to assess the influence of Sn doping, and Sn-Cr codoping on the vibrational properties of single nanowires. Cathodoluminescence (CL) measurements show a Sn-related complex band in the Sn-doped structures. Temperature-dependent and excitation-density-dependent CL indicates that this is a thermally activated emission. In the Sn-Cr codoped samples, the characteristic, very intense Cr^3+ red luminescence emission quenches the bands observed in the Sn-doped samples. Branched, Sn-Cr codoped structures were studied with microphotoluminescence imaging and spectroscopy, and waveguiding behavior was observed along the trunks and branches of these structures., MICINN, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Benefitted from progress on the large-diameter Ga2O3 wafers and Ga2O3 processing techniques, the Ga2O3 power device technology has witnessed fast advances toward power electronics applications. Recently, reports on large-area (ampere-class) Ga2O3 power devices have emerged globally, and the scope of these works have gone well beyond the bare-die device demonstration into the device packaging, circuit testing, and ruggedness evaluation. These results have placed Ga2O3 in a unique position as the only ultra-wide bandgap semiconductor reaching these indispensable milestones for power device development. This paper presents a timely review on the state-of-the-art of the ampere-class Ga2O3 power devices (current up to >100 A and voltage up to >2000 V), including their static electrical performance, switching characteristics, packaging and thermal management, and the overcurrent/overvoltage ruggedness and reliability. Exciting research opportunities and critical technological gaps are also discussed.

This paper reports on the deposition of amorphous and crystalline thin films of Ga2O3 by reactive pulsed direct current magnetron sputtering from a liquid gallium target onto fused (f-) quartz and c plane (c-) sapphire sub-strates, where the temperature of the substrate is varied from room temperature (RT) to 800 degrees C. The deposition rate (up to 37 nm/min at RT on f-quartz and 5 nm/min at 800 degrees C on c-sapphire) is two to five times higher than the data given in the literature for radio frequency sputtering. Deposited onto unheated substrates, the films are X-ray amorphous. Well-defined X-ray diffraction peaks of 13-Ga2O3 start to appear at a substrate temperature of 500 degrees C. Films grown on c-sapphire at temperatures above 600 degrees C are epitaxial. However, the high rocking curve full width at half maximum values of X2.4-2.5 degrees are indicative of the presence of defects. A dense and void-free microstructure is observed in electron microscopy images. Composition analysis show stoichiometry close to Ga2O3 and no traces of impurities. The optical properties of low absorptance (<1%) in the visible range and an optical band gap of approximately 5 eV are consistent with the data in the literature for Ga2O3 films produced by other deposition methods.

This paper reports on the deposition of amorphous and crystalline thin films of Ga2O3 by reactive pulsed direct current magnetron sputtering from a liquid gallium target onto fused (f-) quartz and c plane (c-) sapphire sub-strates, where the temperature of the substrate is varied from room temperature (RT) to 800 degrees C. The deposition rate (up to 37 nm/min at RT on f-quartz and 5 nm/min at 800 degrees C on c-sapphire) is two to five times higher than the data given in the literature for radio frequency sputtering. Deposited onto unheated substrates, the films are X-ray amorphous. Well-defined X-ray diffraction peaks of 13-Ga2O3 start to appear at a substrate temperature of 500 degrees C. Films grown on c-sapphire at temperatures above 600 degrees C are epitaxial. However, the high rocking curve full width at half maximum values of X2.4-2.5 degrees are indicative of the presence of defects. A dense and void-free microstructure is observed in electron microscopy images. Composition analysis show stoichiometry close to Ga2O3 and no traces of impurities. The optical properties of low absorptance (<1%) in the visible range and an optical band gap of approximately 5 eV are consistent with the data in the literature for Ga2O3 films produced by other deposition methods., QC 20230227

Currently, a significant portion (~50%) of global warming emissions, such as CO, are related to energy production and transportation. As most energy usage will be electrical (as well as transportation), the efficient management of electrical power is thus central to achieve the XXI century climatic goals. Ultra‐wide bandgap (UWBG) semiconductors are at the very frontier of electronics for energy management or energy electronics. A new generation of UWBG semiconductors will open new territories for higher power rated power electronics and solar‐blind deeper ultraviolet optoelectronics. Gallium oxide—GaO (4.5–4.9 eV), has recently emerged pushing the limits set by more conventional WBG (~3 eV) materials, such as SiC and GaN, as well as for transparent conducting oxides (TCO), such asInO, ZnO and SnO, to name a few. Indeed, GaO as the first oxide used as a semiconductor for power electronics, has sparked an interest in oxide semiconductors to be investigated (oxides represent the largest family of UWBG). Among these new power electronic materials, AlxGa1‐xO may provide high‐power heterostructure electronic and photonic devices at bandgaps far beyond all materials available today (~8 eV) or ZnGaO (~5 eV), enabling spinel bipolar energy electronics for the first time ever. Here, we review the state‐of‐the‐art and prospects of some ultra‐wide bandgap oxide semiconductor arising technologies as promising innovative material solutions towards a sustainable zero emission society.

Altres ajuts: the ICN2 is funded by the CERCA programme/Generalitat de Catalunya., Currently, a significant portion (~50%) of global warming emissions, such as CO, are related to energy production and transportation. As most energy usage will be electrical (as well as transportation), the efficient management of electrical power is thus central to achieve the XXI century climatic goals. Ultra-wide bandgap (UWBG) semiconductors are at the very frontier of electronics for energy management or energy electronics. A new generation of UWBG semiconductors will open new territories for higher power rated power electronics and solar-blind deeper ultraviolet optoelectronics. Gallium oxide-GaO (4.5-4.9 eV), has recently emerged pushing the limits set by more conventional WBG (~3 eV) materials, such as SiC and GaN, as well as for transparent conducting oxides (TCO), such asInO, ZnO and SnO, to name a few. Indeed, GaO as the first oxide used as a semiconductor for power electronics, has sparked an interest in oxide semiconductors to be investigated (oxides represent the largest family of UWBG). Among these new power electronic materials, AlGaO may provide high-power heterostructure electronic and photonic devices at bandgaps far beyond all materials available today (~8 eV) or ZnGaO (~5 eV), enabling spinel bipolar energy electronics for the first time ever. Here, we review the state-of-the-art and prospects of some ultra-wide bandgap oxide semiconductor arising technologies as promising innovative material solutions towards a sustainable zero emission society.

The use of glassceramics in photocatalysis is an attractive option for the realization of smart optical fibers and self-cleaning windows. Here we present the photocatalytic activity of germanosilicate glasses embedding Ga2O3 nanocrystals prepared by batch melting and glass heat treatment. The powdered material is used for UV-assisted degradation of rhodamine in water. The kinetics show changes after repeated experiments. In the first cycle, the apparent rate is governed by a second-order reaction with a Gaussian-like shape, whereas the second cycle follows a first-order reaction. The modification appears to be correlated with perturbations in the defect population. Photoluminescence has been used to monitor the evolution of such defects. Kinetic data on photoreactions and defect formation have been modelled in a combined frame in which the defect concentration determines the photocatalytic activity. The results prove the photocatalytic ability of the studied glassceramics. Moreover, the general validity of the kinetic model can be of interest for other systems in which the photocatalytic response depends on photoreactive species concentration.

Gallium incorporation in silicate glasses gives rise to compounds in which the nucleation and growth of Ga-oxide nanostructures can be designer controlled so as to obtain a number of functional properties for photonic applications. However, despite planar geometry pertains to a large part of modern technology, no information is available yet on the scalability of Ga-oxide segregation mechanisms in oxide thin films. In fact, incorporated Ga-oxide nanostructures have only been obtained in bulk materials. Here we show that deposition of Ga-alkali-germanosilicate thin films by radiofrequency-plasma sputtering gives rise to Ga-oxide nanostructures incorporated in an amorphous matrix. X-ray diffraction, X-ray reflectivity, small-angle X-ray scattering, and atomic force microscopy data unveil the formation of lenticular nanoaggregates, only a few nm thick, even in as-deposited materials as a result of two-dimensional aggregation of spinel-like Ga2O3 nanoparticles. Importantly, the aggregate size distribution is controlled not only by the temperature but also by the film thickness when it is reduced from 102 nm to only a few nm. The results open the way to the design of oxide-in-oxide thin films with incorporated networks of nanostructures which can act as percolation paths for unconventional electric responses in neuromorphic functional systems.

Temperature-dependent studies of Ga2O3-based heterojunction devices are important in understanding its carrier transport mechanism, junction barrier potential, and stability at higher temperatures. In this study, we investigated the temperature-dependent device characteristics of the p-type gamma-copper iodide (gamma-CuI)/n-type beta-gallium oxide (beta-Ga2O3) heterojunctions, thereby revealing their interface properties. The fabricated gamma-CuI/beta-Ga2O3 heterojunction showed excellent diode characteristics with a high rectification ratio and low reverse saturation current at 298 K in the presence of a large barrier height (0.632 eV). The temperature-dependent device characteristics were studied in the temperature range 273-473 K to investigate the heterojunction interface. With an increase in temperature, a gradual decrease in the ideality factor and an increase in the barrier height were observed, indicating barrier inhomogeneity at the heterojunction interface. Furthermore, the current-voltage measurement showed electrical hysteresis for the reverse saturation current, although it was not observed for the forward bias current. The presence of electrical hysteresis for the reverse saturation current and of the barrier inhomogeneity in the temperature-dependent characteristics indicates the presence of some level of interface states for the gamma-CuI/beta-Ga2O3 heterojunction device. Thus, our study showed that the electrical hysteresis can be correlated with temperature-dependent electrical characteristics of the beta-Ga2O3-based heterojunction device, which signifies the presence of surface defects and interface states.

Gallium incorporation in silicate glasses gives rise to compounds in which the nucleation and growth of Ga-oxide nanostructures can be designer controlled so as to obtain a number of functional properties for photonic applications. However, despite planar geometry pertains to a large part of modern technology, no information is available yet on the scalability of Ga-oxide segregation mechanisms in oxide thin films. In fact, incorporated Ga-oxide nanostructures have only been obtained in bulk materials. Here we show that deposition of Ga-alkali-germanosilicate thin films by radiofrequency-plasma sputtering gives rise to Ga-oxide nanostructures incorporated in an amorphous matrix. X-ray diffraction, X-ray reflectivity, small-angle X-ray scattering, and atomic force microscopy data unveil the formation of lenticular nanoaggregates, only a few nm thick, even in as-deposited materials as a result of two-dimensional aggregation of spinel-like Ga2O3 nanoparticles. Importantly, the aggregate size distribution is controlled not only by the temperature but also by the film thickness when it is reduced from 102 nm to only a few nm. The results open the way to the design of oxide-in-oxide thin films with incorporated networks of nanostructures which can act as percolation paths for unconventional electric responses in neuromorphic functional systems.

In this article, a β-Ga₂O₃ metal-interlayer-semiconductor Schottky barrier diode (MIS-SBD) using Al-reacted aluminum oxide as the interlayer is demonstrated for the first time and compared with conventional metal-semiconductor (MS) Schottky barrier diode (SBD). The aluminum oxide is formed by sputtering a thin Al layer on Ga₂O₃ substrate and then annealed in O₂ at 300 °C. With the insertion of Al-reacted interlayer, the SBD subthreshold swing (SS) is significantly improved to 61 mV/dec with an average current range of >6 orders. Example of atomic layer deposited (ALD) Al₂O₃ as the interlayer is also fabricated and characterized. J-V study corrected by Gaussian distribution model shows that all the samples statistically exhibit similar mean barrier heights (BHs). This indicates that the interlayer hardly affects the electrostatic field and band bending as experienced by carrier injections. C-V study provides different BH results in different sample setups. The result proves that Al-reacted interfacial layer helps eliminate interface degradation as compared with ALD Al₂O₃. Overall, MIS-SBD by Al-reaction method exhibits improved SS, reduced reverse leakage current (I₀), low ideality factor, good on-off ratio (>10⁹), and minimized interface charges as compared with its respective counterparts. The result of this article serves as a promising interface engineering technique for Ga₂O₃-based SBD designs. IEEE

In questa tesi presento il lavoro da me svolto durante il mio dottorato su film vetro-ceramici nanostrutturati contenenti ossido di gallio riguardo alla possibile uso di questa classe di materiali in geometria planare all’interno di dispositivi optoelettronici. Negli ultimi tre anni, le mie ricerche sono state rivolte alla comprensione della relazione fra la presenza delle nanostrutture – analizzate attraverso uno studio strutturale dettagliato grazie a diverse tecniche di microscopia e diffrazione in funzione delle condizioni di deposizioni e trattamenti successivi – e i meccanismi fisici di trasporto di carica e polarizzazione che accadono all’interno di film di ossidi-in-ossidi. Il materiale studiato è stato preparato tramite sputtering a radiofrequenze a partire da un precursore vetroso contenente ossidi di Li, Na, Si, Ga e Ge. Come conseguenza del processo di deposizione abbiamo ottenuto un materiale parzialmente cristallino con nanocristalli ricchi in Ga incorporati nel resto della matrice amorfa. Attraverso la microscopia a forza atomica, la riflessione dei raggi x, la diffrazione 2D dei raggi x, la dispersione 2D dei raggi x a piccoli angoli – anche usando luce di sincrotrone – abbiamo completamente caratterizzato i film nanostutturati a diverse scale di grandezza, da pochi nm a qualche micron. L’analisi dettagliata dei risultati mostra la formazione di molteplici nanocristalli anisotropi di spinello di ossido di gallio con dimensioni di 3 nm, che formano aggregati lenticolari di dimensioni maggiori con differenze significative nelle dimensioni nel piano e fuori dal piano. Come risultato dell’indagine di campioni trattati differentemente, lo studio ha inoltre mostrato che la distribuzione e la morfologia di nanostrutture può essere controllata dalle condizioni della deposizione, dalla durata e dalla temperatura del trattamento termico seguente. Partendo dalla conoscenza delle caratteristiche strutturali, l’attività di ricerca è stata indirizzata verso l’appr, In this thesis I present the work I have carried out during my PhD on Ga-oxide containing nanostructured glass-ceramic films as a potential breakthrough for the implementation of this class of material in planar geometry for applications in the field of optoelectronics. In the last three years, my investigations have been aimed at understanding the relationship between the occurrence of nanostructuring – analysed through a detailed structural studies by means of different microscopy and diffractometric techniques as a function of deposition conditions and post-deposition treatments – and the physical mechanisms of charge transport and polarization taking place in oxide-in-oxide films. The studied material was produced by RF sputtering deposition starting from a glass target of Li, Na, Si, Ga and Ge mixed oxide. As a consequence of the deposition process we have obtained partially crystallized material with Ga-rich nanocrystals incorporated in the remaining amorphous matrix. Through atomic force microscopy, x-ray reflectivity, 2D-x-ray diffraction, 2D-small angle x-ray scattering - also employing synchrotron radiation facilities - we have fully characterized the nanostructured films at different length scales, from few nm to few microns. The detailed analysis of the results shows the formation of multiple anisotropic spinel Ga-oxide nanocrystals with size of about 3 nm, forming larger lenticular aggregates with significant differences between the in-plane and the out-of-plane dimensions. As a result of the investigation of differently treated samples, the study also shows that size distribution and morphology of the nanostructures can be controlled by deposition conditions, duration and temperature of post-deposition thermal treatments. Starting from the knowledge of the structural features, the research activity has been directed to the deep understanding of the charge transport properties resulting from the nanostructured nature of the material, including the Ga2O3

LORENZI, ROBERTO, open, In this thesis I present the work I have carried out during my PhD on Ga-oxide containing nanostructured glass-ceramic films as a potential breakthrough for the implementation of this class of material in planar geometry for applications in the field of optoelectronics. In the last three years, my investigations have been aimed at understanding the relationship between the occurrence of nanostructuring – analysed through a detailed structural studies by means of different microscopy and diffractometric techniques as a function of deposition conditions and post-deposition treatments – and the physical mechanisms of charge transport and polarization taking place in oxide-in-oxide films. The studied material was produced by RF sputtering deposition starting from a glass target of Li, Na, Si, Ga and Ge mixed oxide. As a consequence of the deposition process we have obtained partially crystallized material with Ga-rich nanocrystals incorporated in the remaining amorphous matrix. Through atomic force microscopy, x-ray reflectivity, 2D-x-ray diffraction, 2D-small angle x-ray scattering - also employing synchrotron radiation facilities - we have fully characterized the nanostructured films at different length scales, from few nm to few microns. The detailed analysis of the results shows the formation of multiple anisotropic spinel Ga-oxide nanocrystals with size of about 3 nm, forming larger lenticular aggregates with significant differences between the in-plane and the out-of-plane dimensions. As a result of the investigation of differently treated samples, the study also shows that size distribution and morphology of the nanostructures can be controlled by deposition conditions, duration and temperature of post-deposition thermal treatments. Starting from the knowledge of the structural features, the research activity has been directed to the deep understanding of the charge transport properties resulting from the nanostructured nature of the material, including the Ga2O3, In questa tesi presento il lavoro da me svolto durante il mio dottorato su film vetro-ceramici nanostrutturati contenenti ossido di gallio riguardo alla possibile uso di questa classe di materiali in geometria planare all’interno di dispositivi optoelettronici. Negli ultimi tre anni, le mie ricerche sono state rivolte alla comprensione della relazione fra la presenza delle nanostrutture – analizzate attraverso uno studio strutturale dettagliato grazie a diverse tecniche di microscopia e diffrazione in funzione delle condizioni di deposizioni e trattamenti successivi – e i meccanismi fisici di trasporto di carica e polarizzazione che accadono all’interno di film di ossidi-in-ossidi. Il materiale studiato è stato preparato tramite sputtering a radiofrequenze a partire da un precursore vetroso contenente ossidi di Li, Na, Si, Ga e Ge. Come conseguenza del processo di deposizione abbiamo ottenuto un materiale parzialmente cristallino con nanocristalli ricchi in Ga incorporati nel resto della matrice amorfa. Attraverso la microscopia a forza atomica, la riflessione dei raggi x, la diffrazione 2D dei raggi x, la dispersione 2D dei raggi x a piccoli angoli – anche usando luce di sincrotrone – abbiamo completamente caratterizzato i film nanostutturati a diverse scale di grandezza, da pochi nm a qualche micron. L’analisi dettagliata dei risultati mostra la formazione di molteplici nanocristalli anisotropi di spinello di ossido di gallio con dimensioni di 3 nm, che formano aggregati lenticolari di dimensioni maggiori con differenze significative nelle dimensioni nel piano e fuori dal piano. Come risultato dell’indagine di campioni trattati differentemente, lo studio ha inoltre mostrato che la distribuzione e la morfologia di nanostrutture può essere controllata dalle condizioni della deposizione, dalla durata e dalla temperatura del trattamento termico seguente. Partendo dalla conoscenza delle caratteristiche strutturali, l’attività di ricerca è stata indirizzata verso l’appr, No, open, Remondina, J

Understanding the atomic structure of materials lies at the heart of materials science. Electron microscopy offers myriad techniques to both probe processing-structure-property relationships in materials, and to manipulate those relationships directly. In this thesis, analytical transmission electron microscopy (TEM) was used to investigate two distinct material systems with applications to energy-efficient technologies: wide-bandgap semiconductors and nanocarbon-metal composites. In the first project, TEM and electron energy loss spectroscopy were used to investigate the structure, composition and bonding of metal-oxide-semiconductor devices based on silicon carbide (SiC) and gallium oxide (Ga2O3). The performance of SiC falls short of ideal due to electrically active interfacial defect states. This work confirms that boron doping at the SiC/SiO2 interface is feasible and improves the device channel mobility likely through a stress-relaxation mechanism. Separately, no adverse structural effects were found after antimony ion implantation into the SiC substrate, which independently raises mobility via a counter-doping mechanism. Few atomic-scale studies on Ga2O3 have been reported to date; this thesis aims to bridge the knowledge gap by investigating gate oxide materials and process conditions from a structural perspective. Elevated annealing temperatures reduced interface quality for both SiO2 and Al2O3 gate oxides. Separately, amorphous Al2O3 layers were crystallized under moderate electron irradiation in TEM. One-fourth the dose was required for crystallization with 100-keV electrons compared to 200 keV, indicating an ionization-induced atomic rearrangement mechanism. This unexpected phenomenon will have implications for devices operating in extreme environments. The second project investigated structure-property relationships in novel nano-carbon metal-matrix composites called covetics, which exploit the superior mechanical and electrical properties of carbon nan

Pulsed laser ablation is used to form high-quality silicon-doped β-Ga2O3 films on sapphire by alternatively depositing Ga2O3 and Si from two separate sources. X-ray analysis reveals a single crystallinity with a full width at half maximum for the rocking curve around the (−201) reflection peak of 1.6°. Silicon doping concentration is determined by elastic recoil detection analysis (ERDA), and the best electrical performance is reached at a Si concentration of about 1 × 1020 cm−3, using optimized deposition parameters. It is found that a high crystalline quality and a mobility of about 2.9 cm2 (V s)−1 can be achieved by depositing Si and Ga2O3 from two separate sources. Two types of Schottky contacts are fabricated: one with a pure Pt and one with a PtOx composition. Electrical results from these structures are also presented. © 2020 The Authors. Published by Wiley-VCH GmbH, QC 20201201

Resistive switching effect is observed for a gallium-indium/gallium oxide/graphene junction. The use of a gallium-based liquid metal alloy, in this case, the eutectic gallium-indium with its native gallium oxide skin, directly provides the metal top contact and the oxide layer needed to fabricate a memory. Graphene is used as bottom electrode due to its electrical properties and, importantly, because it prevents the formation of alloys, leading to a stable simple junction. With this structure, the ON/OFF ratio at 0.5 V between the high resistance state (HRS) and low resistance state (LRS) reached is ~ 104 in ambient conditions. The deposition of an additional switching layer is not needed compared to other resistive random access memories, which makes this system less complex to fabricate. The migration of the oxygen atoms of the oxide layer would be intuitively considered the main reason for the modulation of the tunneling junction resistance but, we suggest that this is not the case and instead of that, charge-trapping/detrapping at the very interface may dominate the switching function.

Ga2O3 has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga2O3 power devices stimulated by early demonstrations of high-voltage Ga2O3 field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga2O3 FETs - which have predominantly been lateral devices - for power switching and radiation-hard electronics. The development of vertical Ga2O3 transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed. © 2020 by World Scientific Publishing Co. Pte. Ltd.

Ga2O3 has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga2O3 power devices stimulated by early demonstrations of high-voltage Ga2O3 field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga2O3 FETs-which have predominantly been lateral devices-for power switching and radiation-hard electronics. The development of vertical Ga2O3 transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed. © 2019 World Scientific Publishing Company.

We found that nitrogen (N) and silicon (Si) were unintentionally co-doped in Ga2O3 layers grown by plasma-assisted molecular beam epitaxy (PAMBE), and that the ratio between N and Si could be controlled by O/Ga flux ratio during the growth. Note that N and Si act as a deep acceptor (theoretically predicted) and a shallow donor (experimentally confirmed) in Ga2O3, respectively. Taking advantage of this unique characteristic of PAMBE-grown Ga2O3, normally off operation of Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) was demonstrated. The unintentionally-doped Ga2O3 channel layer of the MOSFETs had N and Si concentrations of 1× 1018 and 2 × 1017 cm-3, respectively, and thus it was considered to behave as a p-type material. The MOSFETs showed a turn-on threshold gate voltage of larger than +8 V, implying formation of an inversion channel in the N-doped Ga2O3 layer. Although the ON-state drain current (Id) remained in the subthreshold regime owing to limited gate voltage swing, the Id ON/OFF ratio exceeded five orders of magnitude. © 1980-2012 IEEE.

Gallium oxide (Ga2O3) has been gaining considerable attention as a representative of ultra-wide bandgap semiconductors. This paper introduces our state-of-the-art Ga2O3 device technologies developed for applications to future power switching electronics. © 2018 GaAs Mantech Incorporated. All Rights Reserved.

The aim of the work was to prepare nanosized In₂O₃ and Ga₂O₃ photocatalysts for degradation of perfluorooctanoic acid (PFOA) in water. Their commercial references along with TiO₂ were used as a comparison basis. The characterization of the materials proved that successful preparation of cubic In₂O₃ and monoclinic β-Ga₂O₃ were achieved via solvothermal and hydrothermal methods, respectively. The effect of different parameters such as catalyst dosage, UV light source and utilization of inorganic oxidant in PFOA treatment were evaluated. In₂O₃, photocatalyst was the most efficient in the degradation of 15 mg L−¹ PFOA under UVB irradiation and synthetic air reaching 27% of degradation, which was 20 percentage points higher than for commercial In₂O₃. This is proposed to be partly due to significantly higher specific surface area of the self-made In₂O₃ and smaller crystallite size and partly due to more efficient absorption of UVB light compared to the other tested materials. Addition of KBrO₃ did not improve the activity of self-made In₂O₃.

The use of passive shutters to control the duration of the light pulses is an important aspect in the miniature and microchip lasers. One of the key spectroscopic characteristics which determine the properties of the material, which can be used as a passive shutter is relaxation time of its bleached state. We describe a device for determination of relaxation time of the bleached state in optical materials by the "pump-probe" method in the sub-mu s time domain. This device allows one to determine relaxation times for materials which absorb at the light wavelength of 1.5 mu m, e.g., materials doped with cobalt ions Co2+. The results of test examinations of the device are described, and the relaxation time of the bleached state of Co2+ ions is measured for a novel material - transparent glass-ceramics with Co2+:Ga2O3 nanophase - amounting to 190 +/- 6 ns., QC 20161124

Optical glassceramics are an important class of functional materials mainly employed in photonic and optoelectronic applications, as well as for advanced fiber optics. Here we present recent results on phase separation processes and optical properties of alkali germanosilicate glasses containing gallium oxide nanoparticles. Samples, with typical composition 7.5Li2O–2.5Na2O–20Ga2O3–35GeO2–35SiO2 (mol%), are obtained from the melt-quenching method. The resulting glasses are completely amorphous, but show phase separation, on the nanometer scale, deriving from liquid–liquid phase separation in the melt. Nanocrystallization of gallium oxide, in its metastable gamma phase, is thermally activated inside the matrix at about 615 °C. Treatment at higher temperature causes the formation of LiGa5O8 polymorph by Li ion diffusion from the surrounding matrix to the nanocrystals. In a second step, a further increment of temperature induces an order-to-disorder LiGa5O8 change that finally dissociates causing the formation of beta-Ga2O3. Neutron scattering, X-ray diffraction analysis, differential scanning calorimetry, and transmission electron microscopy studies have been performed so as to assess nucleation and crystal growth mechanisms. Parallel to morphological studies, we also present optical response of these systems, characterized by a strong UV-excited blue luminescence due to intrinsic defects and its dependence on thermal treatments. - See more at: http://www.european-mrs.com/2015-fall-symposium-w-european-materials-research-society#sthash.pRj5G4Gf.dpuf

Solvothermally synthesized Ga2O3 nanoparticles are incorporated into liquid metal/metal oxide (LM/MO) frameworks in order to form enhanced photocatalytic systems. The LM/MO frameworks, both with and without incorporated Ga2O3 nanoparticles, show photocatalytic activitydue to a plasmonic effect where performance is related to the loading of Ga2O3 nanoparticles. Optimum photocatalytic efficiency is obtained with 1 wt% incorporation of Ga2O3 nanoparticles. This can be attributed to the sub-bandgap states of LM/MO frameworks, contributing to pseudo-ohmic contacts which reduce the free carrier injection barrier to Ga2O3.

Nanoparticles in amorphous oxides are a powerful tool for embedding a wide range of functions in optical glasses, which are still the best solutions in several applications in the ever growing field of photonics. However, the control of nanoparticle size inside the host material is often a challenging task, even more when detrimental effects on light transmittance have to be avoided. Here we show how the process of separation and subsequent nanocrystallization of a Ga-oxide phase can be controlled in germanosilicates - prototypal systems in optical telecommunications - starting from a Ga-modified glass composition designed to favour uniform liquid-liquid phase separation in the melt. Small angle neutron scattering data demonstrate that nanosized structuring occurs in the amorphous as-quenched glass and gives rise to initially smaller nanoparticles, by heating, as in a secondary phase separation. By further heating, the nanophase evolves with an increase of nanoparticle gyration radius, from few nm to a saturation value of about 10 nm, through an initial growing process followed by an Ostwald ripening mechanism. Nanoparticles finally crystallize, as indicated by transmission electron microscopy and x-ray diffraction, as gamma-Ga2O3 - a metastable gallium oxide polymorph. Infrared reflectance and photoluminescence, together with the optical absorption of Ni ions used as a probe, give indication of the underlying interrelated processes of structural change in the glass and in the segregated phase. As a result, our data give for the first time a rationale for designing Ga-modified germanosilicates at the nanoscale, with the perspective of a detailed nanostructuring control.

The overall aim of this thesis was to develop a sol-gel gallium oxide (Ga2O3) coating and to study the phase evolution in coating, and to evaluate theoretically the crystal structure and electrical properties of coating by modelling the intrinsic- and doped-Ga2O3 structure using Materials Studio software, and to solid theoretical result, experimental work was performed and compared with the simulation results. The most stable phase of gallium oxide (β-Ga2O3) is a wide band gap (4.9eV) metal oxide having a wide range of important applications. β-Ga2O3 is thermally and chemically stable at high temperatures and so exhibits very stable operating characteristics over large temperature ranges. The major limitations of this coating arise from it having high resistivity. Monoclinic gallium oxide (β-Ga2O3) is one of the most promising materials for the device applications because of its wide band gap which gives high transparency from the visible into the UV wavelength regions (~260 nm). However, the high electrical resistivity of Ga2O3 coatings is going to be a significant issue making limitation for this coating to be used in optoelectronic devices. Therefore, incorporation of dopants to reduce Ga2O3 resistivity is desirable. To develop Ga2O3 coating, two types of sols were prepared in this work using gallium isopropoxide as the starting precursor. The first sol (Type-I sol) was prepared via an aqueous route based on the method developed by Yoldas for alumina sol-gel coatings. The other sol (Type-II sol) was prepared via a non-aqueous route involving 2-methoxyethanol (MOE) as the solvent. The principle of coating process was the deposition of these sols onto substrate (glass and quartz) by spin coating followed by drying and then heat treating at elevated temperature. The Type-I sol did not gelate during the deposition process as evidenced by the lack of any visible coating on the substrates. In contrast, the Type-II sol produced obvious coatings, albeit wi

Gallium nitride powders were calcined with copper oxide in either air or N2 and analyzed by means of powder X-ray diffraction (XRD), high-resolution parallel illumination (HRTEM) and scanning probe transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDXS), and electron energy loss spectroscopy (EELS) in order to address the structural and electronic effects of Cu-incorporation into GaN. Gallium oxide and multiple copper oxide phases corresponding to the calcination environment were detected. Significant changes in the lattice parameters and electronic structure of the N2-processed GaN indicate incorporation of both copper and oxygen into the GaN lattice as well as changes in the chemical bonding due to the calcinations process. SQUID magnetometer measurements at 300 K demonstrated ferromagnetism in selected samples., QC 20141204

The 0-1 band of the B-2 Sigma(+)-X(2) Sigma(+) system of (GaO)-Ga-69-O-16 and (GaO)-Ga-71-O-16 has been measured and rotationally assigned. Principal molecular constants (T-01, B-0, B-1 , B-e , D-0, D-1 , alpha(e) ) have been obtained.

The 0-1 band of the B-2 Sigma(+)-X(2) Sigma(+) system of (GaO)-Ga-69-O-16 and (GaO)-Ga-71-O-16 has been measured and rotationally assigned. Principal molecular constants (T-01, B-0, B-1 , B-e , D-0, D-1 , alpha(e) ) have been obtained.

A survey of compositions in the GeGaPS system, initially based on the Beta-Sialon system (Si4A12O2N6) was carried out. Most of the samples were prepared by sealed tube melting (using a fused quartz tube) of mixtures of the elements in a rocking furnace. When it was found that these materials are sensitive to oxygen contamination a pressure melting system was constructed in which melts were prepared in vitreous carbon crucibles under an inert gas overpressure. There is a requirement for new materials which are transparent in the 8-14 micro meter wavelength range and have superior thermal shock resistance, toughness, mechanical strength, and abrasion resistance compared to existing materials. The purpose of this work was to evaluate the possibility of preparing sulfide-phosphide analogs of oxynitride glasses and glass ceramics in the GeGaPS system. If the silicon nitride structure could be prepared in this system, large improvements in mechanical properties are expected.

This report describes the initial stages of a program to develop deposited dielectrics for GaAs device applications. Three applications of the dielectrics are being investigated: (1) isolation of control electrodes, (2) passivation of the GaAs surface, and (3) encapsulation of completed circuits. The dielectrics being studied include silicon oxynitride; mixtures of silicon nitrode and germanium nitride; and mixtures of silicon dioxide, gallium oxide, and aluminum oxide. Deposition techniques being employed are pyrolytic chemical vapor deposition, plasma-enhanced deposition, and photochemical deposition. This report describes the apparatus being used for this program and the chemical analysis of preliminary films deposited. No interface state measurements are reported. (Author)

The object of this project is to establish a reliable supply of high quality magnetic bubble materials to support the device work of various Department of Defense agencies. This work encompasses bulk, non-magnetic garnet crystal growth (for use as substrates), substrate polishing and preparation, liquid phase epitaxial growth of high performance magnetic garnet film compositions, chemical vapor deposition of Ga-YIG films, and the investigation of arc-plasma spraying as a technique for preparing magnetic bubble garnet films. Characterization data are given for materials delivered during this phase.

The research program on the preparation of ultra-pure alkali halide single crystals incorporates three interrelated steps: purification, single crystal growth, and characterization and analysis. In the preparation and study of highly perfect specimens of refractory metals, accomplishments were made in four areas: (a) procedures were developed for the growth of single crystals of niobium by the strain-anneal technique and for the study of their structure by x-ray and metallographic methods, (b) measurements were made of the rate of sintering of porosity in the grain boundaries of niobium bicrystals, (c) bicrystals were prepared for the study of the interfacial energy as a function of misorientation, (d) techniques were developed for the measurement of intergranular diffusion in the bicrystals of niobium. Studies on transition metal and intermetallic compound single crystals were concentrated in four main areas: (a) crystal growth kinetics, (b) transition metal crystal preparation, (c) crystal perfection, and (d) purity evaluation., See also AD0443666.

The adsorption of CO on pure as well as Li2O- and Ga2O3-doped zinc oxides was studied at 30C following various oxidative and reductive pre-treatments. The use of a null-reading quartz spring microbalance in combination with an infrared grating spectrometer permitted the simultaneous measurement of amounts adsorbed and infrared transmission. Integrated band intensities thus obtainable for weakly adsorbed CO species were consistent with the proposed dipolar nature of the interaction; both frequencies and intensities varied with pretreatment, but were uniquely dependent on each other irrespective of substrate. A slow oxidation process on pure zinc oxide surfaces resulting in electron donation to the solid was followed by means of the infrared absorption of the free carriers; the oxidation was thought to lead to a surface donor complex of the metal carbonato type, with weakly adsorbed CO molecules playing the part of a reaction intermediate in its formation. The complex itself must be regarded as a possible precursor in the formation of CO2. (Author), Pub. in Proceedings of the International Congress on Catalysis (3rd), Amsterdam, 20-25 Jul 1964. (Copies available only to DDC users).