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An in‐depth investigation of transition metal impurities (Hf, Zr, Nb, and W) is presented as shallow donors in monoclinic Ga2O3 using first‐principles calculations within the framework of density functional theory. A combination of semilocal and hybrid functionals is used to predict their binding energies and hyperfine parameters. The generalized gradient approximation (GGA) allows performing calculations for supercells of up to 2500 atoms, enabling an extrapolation to the dilute limit. The shortcoming of GGA in correctly describing the electron localization is then overcome by the use of the hybrid functional. Results are presented and discussed in light of the application of these transition‐metal elements as shallow donors in Ga2O3 and their identification in the experiment. The methodology applied here can be used in calculations for shallow donors in other systems.

Gallium Oxide (Ga2O3) devices have shown great potential for radiation detection. However, developing Ga2O3 detectors for pulsed radiation monitoring is still challenging, which requires high response sensitivity (R), low noise, high time resolution, and linear outputs. Herein, a vertical p‐NiO/β‐Ga2O3 heterojunction diode (HJD) is fabricated and its performance in X‐ray detection is analyzed. Benefiting from the high quality of the p‐n heterojunction, the HJD exhibits a low‐leakage current density of less than 1.73 × 10−7 A cm−2 at 100 V and features a high R of 7.92 μC Gy−1 cm−2, a low noise equivalent dose rate of 9.14 × 10−12 Gy−1 Hz−0.5 at an X‐ray dose rate of 0.383 Gy s−1, and good linear outputs to X‐ray dose rates from 0.0383 to 1.149 Gy s−1. The conductive process of the HJD detector is dominated by the tunneling mechanism, which leads to a longer response time associated with the trapping and releasing process of the deep‐level traps under the continuous X‐ray illumination. However, the pulsed X‐ray response property shows no significant influence from the slow trapping/releasing process of the traps. As a result, pulsed X‐ray radiation detection with a 50 ns full width is achieved, and the time resolution of the detector is characterized to be 3.31 ns by a 20 ps laser source. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3), with an ultrawide bandgap corresponding to the deep ultraviolet (DUV) range, has attracted significant attention in optical filter‐free photodetectors. In practical terms, DUV photodetectors employed in extreme conditions, for example, flame detection and space exploration, face the challenges of performance degradation caused by high/low‐temperature transformation. Here, DUV photodetectors are tailored with high durability and stability by one‐step‐grown β‐Ga2O3 films via pulsed laser deposition. A high‐oxygen‐pressure scheme effectively addresses the issue of film‐free deposition at specifically high temperatures, facilitating the formation of polycrystalline high‐resistivity β‐Ga2O3 films. As a result, the devices exhibit outstanding performance, including a low dark current (4.4 pA @30 V), high photoresponsivity (147.36 A W−1), and fast response time (3.1/22.6 ms). Additionally, the photoresponse performance shows minimal degradation at high temperatures up to 300 °C and even improves at low temperatures down to −100 °C, ranking it among the most robust DUV photodetectors. The mechanism of photoresponse, involving the exciton formation, bandgap evolution, carrier‐phonon scatter, etc., is also elucidated in a wide temperature range. This work provides an efficient solution for developing robust Ga2O3 DUV photodetectors with excellent performance for extreme‐condition applications. [ABSTRACT FROM AUTHOR]

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

The growing interest for power electronics devices demands suitable materials which can perform in harsh conditions. Gallium oxide (Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$) has shown tremendous potential in high voltage, high temperature, and gassensing applications due to its unique material properties. Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$ is considered to be the next‐generation material for power electronics owing to ultrawide bandgap of 4.5–4.9 eV and high electric field of 8 MV cm−1. These material properties coupled with high‐power figure of merits make Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$ a superior material compared to GaN and SiC. Herein, state‐of‐the‐art development and recent breakthroughs in Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based field‐effect‐ transistors (FETs) highlighting major ongoing research are reviewed. The review describes the material property, band structure, and Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based field‐effect transistors in detail. Some promising applications capitalizing the epitaxial growth techniques along with the characteristics and performance of Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based devices are also explained. The prime objective of this review is to provide an up‐to‐date scientific framework pertaining to this niche emerging research area followed by device processing. This survey reveals the potential of Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based FETs for high‐ voltage and high‐power applications while several critical challenges have to be still overcome. Finally, insights are represented and future perspectives of Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based transistors along with their hetero‐structures are discussed. [ABSTRACT FROM AUTHOR]

Two-dimensional semiconductors (2DSEM) based on van der Waals crystals offer important avenues for nanotechnologies beyond the constraints of Moore's law and traditional semiconductors, such as silicon (Si). However, their application necessitates precise engineering of material properties and scalable manufacturing processes. The ability to oxidize Si to form silicon dioxide (SiO2) was crucial for the adoption of Si in modern technologies. Here, we report on the thermal oxidation of the 2DSEM gallium selenide (GaSe). The nanometer-thick layers are grown by molecular beam epitaxy on transparent sapphire (Al2O3) and feature a centro-symmetric polymorph of GaSe. Thermal annealing of the layers in an oxygen-rich environment promotes the chemical transformation and full conversion of GaSe into a thin layer of crystalline Ga2O3, paralleled by the formation of coherent Ga2O3/Al2O3 interfaces. Versatile functionalities are demonstrated in photon sensors based on GaSe and Ga2O3, ranging from electrical insulation to unfiltered deep ultraviolet optoelectronics, unlocking the technological potential of GaSe nanostructures and their amorphous and crystalline oxides. [ABSTRACT FROM AUTHOR]

The high spatial resolution and contactless optical readout capabilities of luminescence thermometry offer significant advantages in numerous fields, including biomedicine, space exploration and optoelectronics. In addition, robust, reproducible, and accurate temperature measurements are essential in these areas. The ultra‐wide band gap semiconductor material Ga2O3 is a suitable host for optical sensing in harsh environments due to its high stability. In this work, the thermometric operation of Ga2O3:Cr‐based microcavities are evaluated. They are designed as follows: Ga2O3:Cr microwires are encapsulated in multilayers fabricated by atomic layer deposition (ALD), which act as both Bragg reflectors and protective layers for the thermometric sensor. Prior to the ALD encapsulation step, focused ion beam carved trenches at the microwire ends are necessary to accommodate the multilayer coating. The structural and optical properties of the devices are assessed experimentally, analytically and by simulations. The developed microthermometers can be easily calibrated using a cubic polynomial for the temperature‐dependent resonant peak position shift. A better than 0.5 °C temperature resolution and accuracy for temperatures above −80 °C is demonstrated. Additionally, the devices show robustness against excitation laser densities of at least 34 W mm−2, can operate at temperatures up to 600 °C and remain functional in liquids. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) usually fractures in the brittle form, and achieving large plastic deformability to avoid catastrophic failure is in high demand. Here, ε‐Ga2O3 thin films with columnar crystals and partial unoccupied Ga sites are synthesized, and it is demonstrated that the ε‐Ga2O3 at the submicron scale can be compressed to an ultra‐large plastic strain of 48.5% without cracking. The compressive behavior and related mechanisms are investigated by in situ transmission electron microscope nanomechanical testing combined with atomic‐resolution characterizations. The serrated plastic flow and large strain burst are two major deformation forms of ε‐Ga2O3 during compression, which are attributed to the dislocation nucleation and avalanches, formation of new grains, and amorphization. The ultra‐large compressive plasticity of ε‐Ga2O3 thin films at the submicron scale can inspire new applications of Ga2O3 in micro‐ or nano‐ electronic and optoelectronic devices, especially those that require impact resistance during processing or service. [ABSTRACT FROM AUTHOR]

In this study, eutectic gallium–indium alloy (EGaIn) liquid metal is used as the rear electrode for perovskite solar cells (PSCs), where the interfacial properties of the device, particularly the beneficial roles of the surface oxide of the liquid metal, are explored. The findings demonstrate that the native oxide of the EGaIn electrode significantly affects the stability of photovoltaic performance and impedance characteristics including series and shunt resistances. Based on the results, the following hypothesis is formulated: the oxide interlayer serves two crucial functions of a barrier against metal diffusion and a tunnel for enhancing charge extraction and transfer. The results of elemental mapping and trap density calculation support the former function of the hypothesis that the oxide film can effectively prevent metal penetration into the perovskite layer. Furthermore, measurements involving capacitance−voltage and time‐resolved photoluminescence confirm that the oxide film on the liquid metal eliminates the interfacial Schottky barrier, promoting efficient charge extraction and transfer processes. Finally, the investigation is extended to develop flexible PSCs using the EGaIn electrode, which consistently exhibits stable performance during repeated bending cycles. Notably, the EGaIn rear electrode can be readily removed and collected through a straightforward acid treatment, offering a promising avenue for efficient cell recycling. [ABSTRACT FROM AUTHOR]

A split-stepped gate field plate design has been incorporated on a gallium oxide (Ga2O3) metal-oxide semiconductor field-effect transistor (MOSFET). The aim of the present work is to unfold the potential of Ga2O3 MOSFET by enhancing its breakdown limits and also to overcome the challenge of simultaneous improvement in power as well as radio frequency (RF) metrics. An extensive simulation study focusing on analog and RF metrics has been carried out using technology computer-aided design simulations of the proposed device in a calibrated environment, and a comparative analysis of split stepped gate field plate design, shorted stepped gate field plate design, and conventional Ga2O3 MOSFET design has also been performed. The results highlight the superiority of the proposed device, and a substantial enhancement in breakdown voltage (i.e., 106.36% relative increase) and power figure-of-merit (i.e., 282.70% relative increase) has been demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, gallium oxide (Ga2O3) thin films at various substrate temperatures (Ts) were grown on Indium Tin Oxide (ITO), glass, p-type silicon by radio-frequency magnetron sputtering (RFMS). We investigated how structural, morphological and optical properties change with various Ts. XRD results of thin films grown on p-type silicon substrate suggest that crystallinity properties of synthesized thin films strongly depend on the Ts. From SEM and AFM analyses of Ga2O3 thin films grown on p-type silicon substrate, it was observed that when the temperature increased, a porous structure appeared, and the grain size changed depending on the Ts. Moreover, obtained results from the absorption measurements, the bandgap energy of Ga2O3 thin films grown on the p-type silicon substrate decreased with increasing substrate temperature. [ABSTRACT FROM AUTHOR]

Beta-gallium oxide (β-Ga2O3) is a material with a history of research and development spanning about 70 years; however, it has attracted little attention as a semiconductor for a long time. The situation has changed completely in the last ten years, and the world has seen increasing demand for active research and development of both materials and devices. Many of its distinctive physical properties are attributed to its very large bandgap energy of 4.5 eV. Another important feature is that it is possible to grow large bulk single crystals by melt growth. In this article, we first discuss the important physical properties of β-Ga2O3 for electronic device applications, followed by bulk melt growth and thin-film epitaxial growth technologies. Then, state-of-the-art β-Ga2O3 transistor and diode technologies are discussed. [ABSTRACT FROM AUTHOR]

Electron beam techniques have been used to analyze the impact of substrate choice and growth parameters on the compositional and optical properties of tin gallium oxide [(SnxGa1−x)2O3] thin films grown by plasma‐assisted molecular beam epitaxy. Sn incorporation and film quality are found to be highly dependent on growth temperature and substrate material (silicon, sapphire, and bulk Ga2O3) with alloy concentrations varying up to an x value of 0.11. Room temperature cathodoluminescence spectra show the Sn alloying suppressing UV (3.3–3.0 eV), enhancing blue (2.8–2.4 eV), and generating green (2.4–2.0 eV) emission, indicative of the introduction of a high density of gallium vacancies (VGa) and subsequent VGa–Sn complexes. This behavior was further analyzed by mapping composition and luminescence across a cross section. Compared to Ga2O3, the spectral bands show a clear redshift due to bandgap reduction, confirmed by optical transmission measurements. The results show promise that the bandgap of gallium oxide can successfully be reduced through Sn alloying and used for bandgap engineering within UV optoelectronic devices. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) is a promising material for the development of optoelectronic devices due to its array of suitable properties tailored for such applications. This review paper focuses on low-cost fabrication methods, which include spray-pyrolysis and sol–gel (dip-coating, spin-coating). Furthermore, the operation principle of these methods for synthesizing Ga2O3 thin films are summarized. The properties and applications of Ga2O3 produced by these methods are highlighted to emphasize the benefits of such economical techniques. While disadvantages of these methods are not disregarded. Overall, the aim of this review is to offer a starting point for researchers to develop gallium oxide thin films of acceptable properties for specific applications with a low budget. Highlights: The cost-effective methods for gallium oxide (Ga2O3) thin film synthesis are reviewed. Spray-pyrolysis and sol–gel (dip-coating, spin-coating) operation principle is detailed. The advantages and disadvantages of Ga2O3 synthesized using these methods are discussed. Applications of the produced Ga2O3 are emphasized. The benefits of such cost-effective techniques are discussed. This review can be a valuable resource for researchers to engage in using these low-cost techniques. [ABSTRACT FROM AUTHOR]

Thin films of (Y0.06Ga0.94)2O3:Cr were obtained by radio-frequency (RF) ion-plasma sputtering in an argon atmosphere on polycrystalline polycor and amorphous υ-SiO2 substrates. The surface morphology of the films was studied by atomic force microscopy. It was found that during argon annealing of (Y0.06Ga0.94)2O3:Cr thin films on υ-SiO2 substrates, grain growth occurs perpendicular to the substrate surface. The results of studies of the photoluminescence and cathodoluminescence luminescence of the investigated films are presented. It is shown that thin films of (Y0.06Ga0.94)2O3:Cr on υ-SiO2 substrates under photoexcitation emit in the blue region of the spectrum and this luminescence is due to the luminescence of the (Y0.06Ga0.94)2O3 matrix. Under cathodic excitation, the activator luminescence of the Cr3+ ion dominates with a maximum in the region around 700 nm, due to the electronic transitions 4T2 → 4A2. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) is attracting attention as a next-generation semiconductor material for power device because it has a wide energy band gap and high breakdown electric field. We deposited a Sn polymer, poly-tetraallyl tin, on Ga2O3 samples using a disclosed initiated chemical vapor deposition (iCVD) process. The Sn dopant of the Sn polymer layer is injected into the Ga2O3 through a heat treatment process. Diffusion model of Sn into the Ga2O3 is proposed through secondary ion mass spectroscopy analysis and bond dissociation energy. The fabricated device exhibited typical n-type field-effect transistor (FET) behavior. Ga2O3 Sn-doping technology using iCVD will be applied to 3D structures and trench structures in the future, opening up many possibilities in the Ga2O3-based power semiconductor device manufacturing process. [ABSTRACT FROM AUTHOR]

Due to the recent interest in ultrawide bandgap β-Ga2O3 thin films and nanostructures for various electronics and UV device applications, it is important to understand the mechanical properties of Ga2O3 nanowires (NWs). In this work, we investigated the elastic modulus of individual β-Ga2O3 NWs using two distinct techniques – in-situ scanning electron microscopy resonance and three-point bending in atomic force microscopy. The structural and morphological properties of the synthesised NWs were investigated using X-ray diffraction, transmission and scanning electron microscopies. The resonance tests yielded the mean elastic modulus of 34.5 GPa, while 75.8 GPa mean value was obtained via three-point bending. The measured elastic moduli values indicate the need for finely controllable β-Ga2O3 NW synthesis methods and detailed post-examination of their mechanical properties before considering their application in future nanoscale devices.

Abstract We report the growth of bulk β-Ga2O3 crystals based on crystal pulling from a melt using a cold container without employing a precious-metal crucible. Our approach, named oxide crystal growth from cold crucible (OCCC), is a fusion between the skull-melting and Czochralski methods. The absence of an expensive precious-metal crucible makes this a cost-effective crystal growth method, which is a critical factor in the semiconductor industry. An original construction 0.4–0.5 MHz SiC MOSFET transistor generator with power up to 35 kW was used to successfully grow bulk β-Ga2O3 crystals with diameters up to 46 mm. Also, an original diameter control system by generator frequency change was applied. In this preliminary study, the full width at half maximum of the X-ray rocking curve from the obtained β-Ga2O3 crystals with diameters ≤ 46 mm was comparable to those of β-Ga2O3 produced by edge-defined film fed growth. Moreover, as expected, the purity of the obtained crystals was high because only raw material-derived impurities were detected, and contamination from the process, such as insulation and noble metals, was below the detection limit. Our results indicate that the OCCC technique can be used to produce high-purity bulk β-Ga2O3 single crystalline substrate.

This study aimed to investigate the effect of oxidation temperature on the physical properties of β-Ga2O3 grown by thermal oxidation of GaN in the O2 ambient at high oxidation temperatures from 900 to 1400 °C. Notably, the analysis of the oxidation temperatures ranging from 1100 to 1400 °C remains unexplored in the other studies. The effects of the oxidation temperature on the physical properties were investigated via X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy (FESEM). At all oxidation temperatures, XPS results revealed oxygen deficiency. The top FESEM images indicated disordered nanocolumn structures on the surface of the oxide layer, which increased in abundance with oxidation temperatures exceeding 1100 °C. Energy-filtered high-resolution transmission electron microscopy images and the selected area electron diffraction patterns revealed that the top nanocolumns and the oxidized layer comprised polycrystalline β-Ga2O3. Additionally, the cross-sectional lamellae prepared through focused ion beam milling revealed an increase in the thickness of the β-Ga2O3 layer with oxidation temperature. To account for the variations in the oxide layer thickness, the oxidation temperatures were classified into two ranges of 900–1100 °C and 1100–1400 °C for calculating the activation energy. Moreover, this study assumed that the activation energy required for the oxidation process remained constant within each temperature interval. According to Arrhenius's model, the activation energy from 900 to 1100 °C was calculated to be 286.15 kJ/mol (2.97 eV). Furthermore, the activation energy from 1100 to 1400 °C was determined to be 111.33 kJ/mol (1.15 eV).

Line pattern replication process through nanoimprint lithography (NIL) method has been used in numerous of research fields. NIL technology is not yet utilized for displays industry, and we propose an alignment layer of the sol-gel process using NIL. One-dimensionally nanopatterned by polydimethylsiloxane sheets cause surface changes in hybrid SnGaO thin films mixed in a 3:7 ratio, which aligns the liquid crystals (LCs) uniformly in the line pattern direction. These surface changes are confirmed through atomic force microscopy data analysis, and changes in surface shapes for different the curing temperatures in the furnace are analyzed. X-ray photoelectron spectroscopy shows that the chemical composition of the thin films changes according to curing temperatures, and the intensities of SnO and GaO increase exponentially at 200 °C compared to those at 50 °C. Through this, the van der Waals force increases between surface molecules, in the anisotropic direction to help align the LCs. Furthermore, we performed polarized optical microscopy and pre-tilt angle analysis confirm that the LCs are energized uniformly. Finally, the performance of an actual display device transmittance and electro-optical properties; the transmittance of SnGaO is 4.51p% higher than that of the currently commercialized PI-rubbing, and the voltage-transmittance curve is a perfect graph.

We report the growth of bulk β-Ga2O3 crystals based on crystal pulling from a melt using a cold container without employing a precious-metal crucible. Our approach, named oxide crystal growth from cold crucible (OCCC), is a fusion between the skull-melting and Czochralski methods. The absence of an expensive precious-metal crucible makes this a cost-effective crystal growth method, which is a critical factor in the semiconductor industry. An original construction 0.4–0.5 MHz SiC MOSFET transistor generator with power up to 35 kW was used to successfully grow bulk β-Ga2O3 crystals with diameters up to 46 mm. Also, an original diameter control system by generator frequency change was applied. In this preliminary study, the full width at half maximum of the X-ray rocking curve from the obtained β-Ga2O3 crystals with diameters ≤ 46 mm was comparable to those of β-Ga2O3 produced by edge-defined film fed growth. Moreover, as expected, the purity of the obtained crystals was high because only raw material-derived impurities were detected, and contamination from the process, such as insulation and noble metals, was below the detection limit. Our results indicate that the OCCC technique can be used to produce high-purity bulk β-Ga2O3 single crystalline substrate. [ABSTRACT FROM AUTHOR]

An in‐depth investigation of transition metal impurities (Hf, Zr, Nb, and W) is presented as shallow donors in monoclinic Ga2O3 using first‐principles calculations within the framework of density functional theory. A combination of semilocal and hybrid functionals is used to predict their binding energies and hyperfine parameters. The generalized gradient approximation (GGA) allows performing calculations for supercells of up to 2500 atoms, enabling an extrapolation to the dilute limit. The shortcoming of GGA in correctly describing the electron localization is then overcome by the use of the hybrid functional. Results are presented and discussed in light of the application of these transition‐metal elements as shallow donors in Ga2O3 and their identification in the experiment. The methodology applied here can be used in calculations for shallow donors in other systems. [ABSTRACT FROM AUTHOR]

As an emerging wide-bandgap semiconductor material, β-Ga 2 O 3 has extensive application prospect in high power operating environments due to its excellent electrical properties, but low thermal conductivity and anisotropy bring challenges in device heat dissipation. Heterogeneous integration of β-Ga 2 O 3 with high thermal conductivity substrates might improve thermal dissipation efficiency and device operational stability. However, heterogeneous integration introduces thermal boundary resistance (TBR) between the β-Ga 2 O 3 and the substrate, and it is necessary to investigate proper heterogeneous integration processes to reduce the TBR. In this work, we compare the thermal boundary conductance (TBC) between Ga 2 O 3 and different semiconductors with the Acoustic Mismatch Model (AMM) and Diffusion Mismatch Model (DMM). Molecular dynamics (MD) simulations show that the [010] crystallographic direction of β-Ga 2 O 3 exhibited the highest thermal conductivity and higher TBC with most semiconductors except BN and Diamond. To enhance the thermal transport between β-Ga 2 O 3 and the most widely used SiC substrate, SiO 2 thin film is introduced as an interlayer, and the TBC is enhanced by 3.7 folds. The SiO 2 interlayer can bridge the vibration between β-Ga 2 O 3 and SiC by improving the overlap energy and phonon participation ratio. These research findings provide guides for the selection of substrates and interlayers in heterogeneous integration for β-Ga 2 O 3 device thermal management. [ABSTRACT FROM AUTHOR]

For the first time, nanostructured thin films of the β-Ga2O3−GaN system have been obtained by plasma-enhanced chemical vapor deposition (PECVD) on c-plane sapphire substrates. High-purity gallium metal, as well as high-purity gaseous nitrogen and oxygen, were used as sources of macrocomponents. Low-temperature nonequilibrium plasma of an inductively coupled RF (40.68 MHz) discharge at reduced pressure (0.01 torr) was the initiator of chemical transformations between the reactants. A mixture of oxygen and nitrogen was used as a plasma-forming gas. The plasma-chemical process was studied using optical emission spectroscopy (OES). The resulting β-Ga2O3−GaN thin films with a GaN content of 2 to 7% were characterized by various analytical methods. [ABSTRACT FROM AUTHOR]

An in‐depth investigation of transition metal impurities (Hf, Zr, Nb, and W) is presented as shallow donors in monoclinic Ga2O3 using first‐principles calculations within the framework of density functional theory. A combination of semilocal and hybrid functionals is used to predict their binding energies and hyperfine parameters. The generalized gradient approximation (GGA) allows performing calculations for supercells of up to 2500 atoms, enabling an extrapolation to the dilute limit. The shortcoming of GGA in correctly describing the electron localization is then overcome by the use of the hybrid functional. Results are presented and discussed in light of the application of these transition‐metal elements as shallow donors in Ga2O3 and their identification in the experiment. The methodology applied here can be used in calculations for shallow donors in other systems. [ABSTRACT FROM AUTHOR]

As gallium oxide-based heterojunction devices gain prominence, low-resistance contacts to aluminum gallium oxide material are of increasing importance for high performance and access to modulation doped layers. Here, the activation of ion-implanted silicon donors is investigated as a function of donor density from 5 × 1018 cm−3 to 1 × 1020 cm−3, activation anneal duration from 6 s to 600 s, and activation temperature from 900°C to 1140°C. Importantly, ohmic behavior was achievable across a reasonably wide process window at moderate to high doping concentrations. Specific contact resistance of 1 × 10−3 Ω cm2 and sheet resistance of 2.8 kΩ/□ were achieved for a 60 nm-deep 1 × 1020 cm−3 box implant after activation at 1000°C for 6 s with standard Ti/Au contacts. Under these conditions, an activation efficiency of 7% was observed with Hall mobility of ~32 cm2/Vs. Furthermore, we demonstrate a Schottky diode formed of implanted material with a rectification ratio > 106 and further confirm the Hall carrier density results using capacitance–voltage profiling analysis. Finally, we show the significant impact of anneal duration and the potential for deleterious over-annealing which reduces the active carrier density, mobility, and resultant material conductivity. [ABSTRACT FROM AUTHOR]

Platinum oxide (PtOx) Schottky contacts on degenerately doped β-Ga2O3 substrates show an increased barrier height of 85% and 64% when compared to nickel and platinum Schottky contacts, respectively. At low reverse voltage bias, the reverse leakage current of the PtOx Schottky barrier diodes was approximately 5–6 orders of magnitude lower than the reference evaporated Ni and Pt Schottky contacts. PtOx Schottky contacts were deposited using reactive sputtering on highly doped (8 × 1018 cm−3) ( 2 ¯ 01 ) β-Ga2O3:Sn substrates grown by the edge-defined film-fed growth (EFG) method. All Schottky metals were capped with evaporated Au. Capacitance–voltage and temperature-dependent current–voltage measurements were performed in order to extract the barrier height of the PtOx Schottky contact. Analysis of the diode ideality factors reveal that the PtOx Schottky contacts on highly doped β-Ga2O3 do not follow the thermionic field emission model and are impacted by inhomogeneous barrier height distribution. This work highlights the significance of PtOx Schottky contacts for β-Ga2O3-based power devices as a means for reducing leakage current. This work also holds relevance for low-voltage applications, where Schottky contacts for degenerately doped semiconductors can enable new electronic device applications. [ABSTRACT FROM AUTHOR]

A novel and promising way for creating nanomaterials based on gallium oxide is the ion synthesis of Ga2O3 nanocrystals in a SiO2/Si dielectric matrix. The properties of nanocrystals are determined by the conditions of ion synthesis—the parameters of ion irradiation and post-implantation heat treatment. In this work, the light-emitting properties of Ga2O3 nanocrystals were studied depending on the temperature and annealing atmosphere. It was found that annealing at a temperature of 900 °C leads to the appearance of intense luminescence with a maximum at ~480 nm caused by the recombination of donor–acceptor pairs. An increase in luminescence intensity upon annealing in an oxidizing atmosphere is shown. Based on data from photoluminescence excitation spectroscopy and high-resolution transmission electron microscopy, a hypothesis about the possibility of the participation of a quantum-size effect during radiative recombination is proposed. A mechanism for the formation of Ga2O3 nanocrystals during ion synthesis is suggested, which makes it possible to describe the change in the luminescent properties of the synthesized samples with varying conditions of post-implantation heat treatment. [ABSTRACT FROM AUTHOR]

Thin-film Ga2O3-based solar- and visible-blind photodetectors (PDs) stand at the forefront of future applications, with their performance closely tied to film quality. Employing radio frequency magnetron sputtering, we deposited an intrinsic Ga2O3 thin film onto a double-throw (0001) sapphire substrate at a substrate temperature of 500 °C for 10 min. Subsequently, using the intrinsic Ga2O3 thin film as the substrate and maintaining constant process parameters, including background vacuum, working pressure, growth temperature, sputtering power, and duration, we introduced N2 at various flow rates (0, 5, 10, 15, 20, and 25 sccm) for the reactive sputtering growth of nitrogen-doped amorphous Ga2O3 thin films. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-Vis spectrophotometry, and Hall effect measurements were utilized to probe the impact of N2 flow rate on the growth rate, surface morphology, elemental composition, crystallization quality, and optical characteristics, and electrical properties of the Ga2O3 thin films. With increasing N2 flow rate, the films exhibited a notable redshift of the absorption edge, accompanied by a decrease in optical band gap. Hall effect measurements confirmed the stable p-type conductivity of the nitrogen-doped Ga2O3 thin films. Subsequently, metal-semiconductor-metal-type PDs were fabricated using the nitrogendoped Ga2O3 thin films. These PDs demonstrated heightened sensitivity to 365 nm near-UV light, boasting a remarkable response of 1.32 × 10² A/W and a high response speed of 0.028/0.17 s. [ABSTRACT FROM AUTHOR]

The optical absorption coefficient is one of the fundamental properties of semiconductors and is critical to the development of optical devices. Herein, a revival of the constant photocurrent method is presented to measure sub‐bandgap absorption in wide bandgap semiconductor films. The method involves maintaining a constant photocurrent by continually adjusting the impinging photon flux across the energy spectrum. Under such conditions, the reciprocal of the photon flux for uniformly absorbed light is proportional to the absorption coefficient. This method is applied to α‐Ga2O3 and reveals that it can access the absorption coefficient from 1 × 105 cm−1 at the band edge (5.3 eV) to 0.8 cm−1 close to mid‐bandgap (2.7 eV). Changes in the steepness of the absorption curve in the sub‐bandgap region are in excellent agreement with defect states of α‐Ga2O3 reported by deep level transient spectroscopy, indicating that the technique shows promise as a probe of energetically distributed defect states in thin film wide bandgap semiconductors. [ABSTRACT FROM AUTHOR]

Phosphate glasses are known for their wide applications in the field of optical fiber, lasers, seals and sensors. Glass system containing (40-x) ZnO-xGa2O3-50P2O5- Na2O, where x=0 to 10mol % were prepared. The effect of gallium oxide on the properties of these glasses were studied. To observe the structure of prepared phosphate glasses FTIR was used under the wavelength range of 400-4000 cm-1. The prominent peaks appeared in region 400 cm-1 to 2500 cm-1. The glasses were transparent up to 1500 cm-1 which make them suitable in the field of lasers. The FTIR also confirmed that Q2 structure dominates these glasses. [ABSTRACT FROM AUTHOR]

The optical absorption coefficient is one of the fundamental properties of semiconductors and is critical to the development of optical devices. Herein, a revival of the constant photocurrent method is presented to measure sub‐bandgap absorption in wide bandgap semiconductor films. The method involves maintaining a constant photocurrent by continually adjusting the impinging photon flux across the energy spectrum. Under such conditions, the reciprocal of the photon flux for uniformly absorbed light is proportional to the absorption coefficient. This method is applied to α‐Ga2O3 and reveals that it can access the absorption coefficient from 1 × 105 cm−1 at the band edge (5.3 eV) to 0.8 cm−1 close to mid‐bandgap (2.7 eV). Changes in the steepness of the absorption curve in the sub‐bandgap region are in excellent agreement with defect states of α‐Ga2O3 reported by deep level transient spectroscopy, indicating that the technique shows promise as a probe of energetically distributed defect states in thin film wide bandgap semiconductors. [ABSTRACT FROM AUTHOR]

As a potential electrode material for lithium-ion batteries, Ga2O3 has high theoretical specific capacity and low lithium storage potential. Still, the bulk expansion efficiency and poor reaction kinetics during the reaction process hinder performance improvement. This paper successfully synthesised the Ga2O3 NPs@CF composite electrode with network core–shell structure using the electrospinning method. Carbon coating effectively alleviates the volume expansion of Ga2O3 during the reaction process. The carbon fibre network structure provides more transport channels for ions, and the Ga2O3 NPs@CF composite electrode shows excellent performance. In the long cycle test, after 500 cycles of 0.5 A/g, the discharge capacity reached 611.04mAh/g, and the capacity retention was 99.8%. At the current density of 0.1 ~ 2A/g, after a periodic cycle, when restored to 0.1A/g, the capacity remains at a high reversible capacity of 677.8mAh/g. [ABSTRACT FROM AUTHOR]

Atomic layer deposition was applied on mesoporous silica to synthesize a highly dispersed gallium oxide catalyst. This system was used as starting material to investigate different loadings of nickel in the dehydrogenation of propane under industrially relevant, Oleflex‐like conditions. The formation of NiGa alloys was confirmed by X‐ray diffraction analysis and electron microscopy. Surprisingly, the nanoalloys enhanced the selectivity towards C3H6 while decreasing the tendency for coking. Herein, in situ thermogravimetry, and measured mass fractions of carbon revealed that the coking rate was reduced by over 50 % compared to the pristine gallium oxide. Generally, the increased selectivity can be explained by the partial hydrogenation and reduction of the gallium oxide surface. The optimum temperature for the removal of deposited carbon was evaluated by a temperature programmed oxidation. Finally, the best‐performing Ni−GaOx catalyst was employed in a cycled experiment with periodic reaction and regeneration tests. After regeneration, the selected Ni−GaOx catalyst provided a higher yield of propylene compared to the unmodified gallium oxide. [ABSTRACT FROM AUTHOR]

Achieving broad light absorption and high carrier separation efficiency is crucial for wide‐bandgap semiconductors to enable broadband photodetection applications. Here, amorphous gallium oxide nanosheets feature with broad absorption and spin polarization Wis synthesized, and assembled with graphene and p‐Si, realizing UV‒vis‒NIR photodetection. Extended X‐ray absorption fine structure reveals that a‐GaOx NSs possess lower tetrahedral Ga occupation (10%) compared to crystalline β‐Ga2O3 (50%). UV‒vis‒NIR diffuse reflectance spectra and magnetic hysteresis loops demonstrate broad absorption and weak ferromagnetism of a‐GaOx NSs, respectively. Density functional theory calculation further reveals sub‐gap states and spin polarization in a‐GaOx NSs. Moreover, combined with Mott–Schottky curves, photoluminescence and time‐resolved photoluminescence spectra inferred the effective suppression of carrier recombination via spin polarization of a‐GaOx NSs. The graphene/a‐GaOx NSs/p‐Si photodetector incorporates a back‐to‐back rectifying junction, acquiring a dark current as low as 63 pA. All photogenerated carriers are in the depletion region of the photodetector favouring efficient charge separation. This photodetector exhibits a response time of τrise<60 ms and τfall<120 ms, and high specific detectivity 1013 Jones over 254–1064 nm light. [ABSTRACT FROM AUTHOR]

Gallium oxide (β‐Ga2O3) is a prominent representative of the new generation of wide‐bandgap semiconductors, boasting a bandgap of ≈4.9 eV. However, the growth process of β‐Ga2O3 materials introduces unavoidable oxygen vacancies (Vo), leading to persistent photoconductivity (PPC), a phenomenon that severely hinders device performance. In this study, an innovative approach is successfully developed by introducing high p‐orbital energy nitrogen (N). This leads to the formation of a hybridized state with O 2p orbitals in β‐Ga2O3, resulting in the creation of GaON and suppressing the electrical activity of Vo. Through meticulous experimentation and advanced computational methods, a comprehensive and insightful explanation of the regulation and mechanism underlying this passivation process is offered. Moreover, pn‐junction solar‐blind photodetectors are engineered using hybridized GaON thin films with p‐type CuPc. These photodetectors demonstrate exceptional characteristics, including ultra‐low dark current (10−14 A), high photo‐to‐dark current ratio (106), and rapid decay speed (0.008 s) even at zero bias. Based on these advancements, a solar‐blind ultraviolet communication system is designed, featuring straightforward and reliable encoding, easy implementation, and robust anti‐interference capabilities. [ABSTRACT FROM AUTHOR]

Ga2O3 is an ultra‐wide‐bandgap semiconductor that is receiving considerable attention due to its promising applications in high‐frequency, high‐power and high‐temperature settings. It can be prepared by calcinating the α‐GaOOH phase at high temperatures. Understanding the significance of hydroxyl groups in α‐GaOOH, dehydroxylation and the structural transition at high temperatures has become a key aspect of preparing high‐quality α‐Ga2O3 crystals, but the underlying mechanism remains unknown. In this research, α‐GaOOH nanorods were hydrothermally synthesized and the structural evolution of α‐GaOOH investigated at high temperatures by in situ X‐ray diffraction. The hydroxyl group in α‐GaOOH squeezes Ga3+ from the center of the [GaO6] octahedron, resulting in deformed [GaO6] octahedra and significant microstrain in α‐GaOOH. The hydroxyl groups are peeled off from α‐GaOOH when the temperature exceeds 200°C, resulting in contraction along the c‐axis direction and expansion along the a‐axis direction of α‐GaOOH. When the temperature exceeds 300°C, the Ga—O bond inside the double chains preferentially breaks to generate square‐wave‐like octahedron chains, and the neighboring chains repack to form hexagonal‐like octahedron layers. The octahedron layers are packed up and down by electrostatic interaction to generate the α‐Ga2O3 structure. This work highlights the role of hydroxyl groups in α‐GaOOH, dehydroxylation and the structural transition on the atomic scale, providing valuable guidelines for the fabrication of high‐quality α‐Ga2O3 crystals. [ABSTRACT FROM AUTHOR]

The monoclinic β-polymorph of gallium oxide is a semiconductor with an ultra-wide bandgap. It is becoming increasingly significant for various technological applications. We have investigated the tracer self-diffusion of oxygen in β-Ga2O3 single crystals as a function of the oxygen partial pressure (2, 20 and 200 mbar) at a temperature of 1375 °C. Isotopically enriched 18O2 gas was used as a tracer source and secondary ion mass spectrometry to analyze depth profiles. We observed that, with decreasing oxygen partial pressure, the diffusivities at a given temperature increase significantly. We suggest that this behaviour can be explained by a change in the diffusion mechanism from oxygen interstitials to oxygen vacancies. [ABSTRACT FROM AUTHOR]

The development of sophisticated solar-blind photodetector devices is being motivated by the increasing need for solar-blind sensors with remarkable photosensitive qualities. This work is a modeling and simulation of electrical and optical properties of a Schottky photodetector based on gallium oxide (Ga2O3), one of the most promising wide-band-gap material. It focuses on the optimization of the device structure design, assumed fully transparent to visible light. In addition, analysis of electrical and optical properties of β-Ga2O3-based photodetector was carried out to accurately describe physical phenomenon through the semiconductor bulk. The impact of several parameters of the device on its performances is such as layer thickness, doping concentration, and electron affinity, anode work function and different cathode contact materials. Besides that, and for more understanding the real behaviors within different layers of the photodetector, diverse optical parameters were varied, for instance the light power intensity and the spectral response by changing the optical wavelength. The obtained results show a promising performance enhancement compared to previous works, for instance the photo to dark current ratio of 3 × 104, the good spectral responsivity in UV light illumination [250–350 nm], in addition to the relatively high detectivity of 2.5 × 109 (Jones). [ABSTRACT FROM AUTHOR]

Polarization-sensitive photodetection and imaging have great application value in fields such as polarization division multiplexing optical communication, remote sensing, near-field imaging and military monitoring. Pursuing a high polarization ratio has always been the research hotspot in polarization-sensitive photodetectors. In this paper, we report a compression strain enhanced polarization ratio in β-gallium oxide (β-Ga2O3) single crystal flake. A rigorous crystallographic analysis confirmed its high crystalline quality and orientation. Angle-resolved polarization Raman spectroscopy (ARPRS) was adopted to study the anisotropy of its optical properties. Extensive ARPRS measurements and theoretical calculation consistently demonstrate the strong optical anisotropy in the high-quality β-Ga2O3 flake. A polarization ratio of 0.96 was obtained in the flat β-Ga2O3 flake. Furthermore, mechanical strain of ±0.7% was introduced into β-Ga2O3. An increased polarization ratio of 0.98 was achieved in the case of 0.7% compression strain, which is, to the best of our knowledge, the highest value for UVC polarization-sensitive photodetectors. That corresponds to an improved polarization rejection ratio of 100. This work proposed a new path towards improving polarization sensitivity by applying strain engineering in the active material. [ABSTRACT FROM AUTHOR]

During the past decade, Gallium Oxide (Ga2O3) has attracted intensive research interest as an ultra-wide-bandgap (UWBG) semiconductor due to its unique characteristics, such as a large bandgap of 4.5–4.9 eV, a high critical electric field of ~8 MV/cm, and a high Baliga's figure of merit (BFOM). Unipolar β-Ga2O3 devices such as Schottky barrier diodes (SBDs) and field-effect transistors (FETs) have been demonstrated. Recently, there has been growing attention toward developing β-Ga2O3-based heterostructures and heterojunctions, which is mainly driven by the lack of p-type doping and the exploration of multidimensional device architectures to enhance power electronics' performance. This paper will review the most recent advances in β-Ga2O3 heterostructures and heterojunctions for power electronics, including NiOx/β-Ga2O3, β-(AlxGa1−x)2O3/β-Ga2O3, and β-Ga2O3 heterojunctions/heterostructures with other wide- and ultra-wide-bandgap materials and the integration of two-dimensional (2D) materials with β-Ga2O3. Discussions of the deposition, fabrication, and operating principles of these heterostructures and heterojunctions and the associated device performance will be provided. This comprehensive review will serve as a critical reference for researchers engaged in materials science, wide- and ultra-wide-bandgap semiconductors, and power electronics and benefits the future study and development of β-Ga2O3-based heterostructures and heterojunctions and associated power electronics. [ABSTRACT FROM AUTHOR]

In this work, the possibility of using different generations of $\beta$-Ga2O3 as an ultra-wide-bandgap power semiconductor device for high power converter applications is explored. The competitiveness of $\beta$-Ga2O3 for power converters in still not well quantified, for which the major determining factors are the on-state resistance, $R_{\text{ON}}$, reverse blocking voltage, $V_{\text{BR}}$, and the thermal resistance, $R_{\text{th}}$. We have used the best reported device specifications from literature, both in terms of reports of experimental measurements and potential demonstrated by computer-aided designs, to study power converter performance for different device generations. Modular multilevel converter-based voltage source converters are identified as a topology with significant potential to exploit these device characteristics. The performance of MVDC & HVDC converters based on this topology have been analysed, focusing on system level power losses and case temperature rise at the device level. Comparisons of these $\beta$-Ga2O3 devices are made against contemporary SiC-FET and Si-IGBTs. The results have indicated that although the early $\beta$-Ga2O3 devices are not competitive to incumbent Si-IGBT and SiC-FET modules, the latest experimental measurements on NiO$_\mathrm{X}$/$\beta$-Ga2O3 and $\beta$-Ga2O3/diamond significantly surpass the performance of incumbent modules. Furthermore, parameters derived from semiconductor-level simulations indicate that the $\beta$-Ga2O3/diamond in superjunction structures delivers even superior performance in these power converters.

Collision cascade density is one of the most important parameters that determine radiation damage accumulation in semiconductors under ion bombardment. We perform calculation of collision cascade parameters formed in β-Ga2O3 by irradiation with 1.3 keV/amu atomic F, P, and molecular PF4 ions using two different methods: the method considering sub-cascade formation, and by calculation an average number of vacancies in spheres of fixed radius. The calculated results are compared with experimental data on damage accumulation in β-Ga2O3 under irradiation with aforementioned ions. It is shown that both methods qualitatively predict the effect of collision cascade density on radiation damage accumulation in gallium oxide. Fractal nature of cascades formed in β-Ga2O3 is established, corresponding fractal dimension is calculated. [ABSTRACT FROM AUTHOR]

The synthesis of nanometer‐thick (≈3 nm) gallium oxynitride (GaOxNy) layers with a variable stoichiometry is reported. The approach primarily exploits the liquid metal chemistry (LMC) technique and promises easier integration of 2D materials onto photonic devices compared to traditional top‐down and bottom‐up methods. The fabrication follows a two‐step process, involving first liquid metal‐based printing of a nanometer‐thick layer of gallium oxide (Ga2O3), followed a plasma‐enhanced nitridation reaction. Control over nitridation parameters (plasma power, exposure time) allows adjustment of the GaOxNy layer's composition, granting access to compounds with distinct optical properties (e.g., a 20% index variation), as demonstrated by ellipsometry and density functional theory (DFT) simulations. DFT provides a microscopic understanding of the effect of the bond polarization and crystallinity on the optical properties of GaOxNy compounds. These findings expand the knowledge of ultrathin GaOxNy alloys, which are poorly studied with respect to their gallium nitride (GaN) and Ga2O3 counterparts. They also represent an essential step toward integrating such 2D materials into photonic chips and offer new opportunities to improve the performance of hybrid optoelectronic devices. [ABSTRACT FROM AUTHOR]

The influence of various energetic particles and electron injection on the transport of minority carriers and non-equilibrium carrier recombination in Ga2O3 is summarized in this review. In Ga2O3 semiconductors, if robust p-type material and bipolar structures become available, the diffusion lengths of minority carriers will be of critical significance. The diffusion length of minority carriers dictates the functionality of electronic devices such as diodes, transistors, and detectors. One of the problems in ultrawide-bandgap materials technology is the short carrier diffusion length caused by the scattering on extended defects. Electron injection in n- and p-type gallium oxide results in a significant increase in the diffusion length, even after its deterioration, due to exposure to alpha and proton irradiation. Furthermore, post electron injection, the diffusion length of an irradiated material exceeds that of Ga2O3 prior to irradiation and injection. The root cause of the electron injection-induced effect is attributed to the increase in the minority carrier lifetime in the material due to the trapping of non-equilibrium electrons on native point defects. It is therefore concluded that electron injection is capable of "healing" the adverse impact of radiation in Ga2O3 and can be used for the control of minority carrier transport and, therefore, device performance. [ABSTRACT FROM AUTHOR]

Resistive metal/β-Ga2O3/metal structures with different interelectrode distances and electrode topologies were investigated. The oxide films were deposited by radio-frequency magnetron sputtering of a Ga2O3 (99.999%) target onto an unheated sapphire c-plane substrate (0001) in an Ar/O2 gas mixture. The films are sensitive to ultraviolet radiation with wavelength λ = 254. Structures with interdigital electrode topology have pronounced persistent conductivity. It is shown that the magnitude of responsivity, response time τr, and recovery time τd are determined by the concentration of free holes p involved in recombination processes. For the first time, it is proposed to consider hole trapping both by surface states Nts at the metal/Ga2O3 interface and by traps in the bulk of the film. [ABSTRACT FROM AUTHOR]

This work reports on the properties of heterojunctions consisting of n-type Ga2O3 layers, deposited using ultrasonic spray pyrolysis at high temperature from water-based solution, combined with p-type NiO and Cu2O counterparts, deposited by radio frequency and reactive, direct-current magnetron sputtering, respectively. After a comprehensive investigation of the properties of the single layers, the fabricated junctions on indium tin oxide (ITO)-coated glass showed high rectification, with an open circuit voltage of 940 mV for Ga2O3/Cu2O and 220 mV for Ga2O3/NiO under simulated solar illumination. This demonstrates in praxis the favorable band alignment between the sprayed Ga2O3 and Cu2O, with small conduction band offset, and the large offsets anticipated for both energy bands in the case of Ga2O3/NiO. Large differences in the ideality factors between the two types of heterojunctions were observed, suggestive of distinctive properties of the heterointerface. Further, it is shown that the interface between the high-temperature-deposited Ga2O3 and the ITO contact does not impede electron transport, opening new possibilities for the design of solar cell and optoelectronic device architectures. [ABSTRACT FROM AUTHOR]