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Abstract Photodetectors play a crucial role in converting light signals into electrical signals and have significant applications in various fields such as communications, imaging, and sensing. However, the fabrication of a photodetector is a complex process that involves precise control of surface preparation, lithography, and deposition techniques. Here the study demonstrates that GaN/Ga2O3 heterojunctions can be fabricated utilizing laser processing to transform the surface of GaN into Ga2O3. The GaN/Ga2O3 heterojunctions exhibit good reproducibility, uniformity, and ability to operate under zero bias, with a responsivity of 110.22 mA W−1, a detection rate of 5.56 × 1011 jones, and an external quantum efficiency of 42.34%. Moreover, an 8 × 8 photodetector array based on GaN/Ga2O3 heterojunction is fabricated via laser writing and is demonstrated to have ultraviolet imaging capabilities. This report presents the pioneering fabrication of a photodetector array using laser writing. The findings offer a versatile and scalable approach for the production of large‐area heterojunction photodetector arrays.

It remains a big challenge to synthesize two-dimensional (2D) GaN material for applications in power nanodevices. Traditional synthetic methods require complex equipment and processes and time consuming. Here, we reported a two-step route to prepare polycrystalline 2D GaN film. The amorphous ultrathin Ga2O3 film was first exfoliated from the surface of liquid gallium. In a vapor phase reaction, 2D Ga2O3 film was then converted into 2D GaN film while maintaining the 2D morphology. Raman and high-resolution transmission electron microscope (HRTEM) analysis implies the successful synthesis of wurtzite-type GaN ultrathin film. This simple strategy proposed in this work will provide more opportunities for applications of GaN ultrathin film in many devices. [ABSTRACT FROM AUTHOR]

The review presents systematization and analysis of experimental data on nanoindentation (NI) of a whole class of new materials, namely, wide-gap AlN, GaN, AlGaN, and β-Ga2O3 heterostructures formed on a hybrid substrate of a new SiC/Si type, which were synthesized by the method of coordinated atom substitution. The deformational and mechanical properties of the investigated materials are described in detail. The methodology of the NI is described, and both advantages and disadvantages of the NI method are analyzed. The description of the apparatus, with the help of which the experiments on NI were carried out, is given. The basic provisions of a new model for describing the deformation properties of a nanoscale rigid two-layer structure on a porous elastic base are described. An original method of visualization of residual (after mechanical interaction) deformation in transparent and translucent materials is described. Experimentally determined values of elastic moduli and hardness of SiC nanoscale layers on Si formed by the method of coordinated substitution on three main crystal planes of Si, namely, (100), (110), and (111), and elastic moduli and characteristics (elastic modulus, hardness, strength) of surface layers of semiconductor heterostructures AlN/SiC/Si, AlGaN/SiC/Si, AlGaN/AlN/SiC/Si, GaN/SiC/Si, and GaN/AlN/SiC/Si grown on SiC/Si hybrid substrates are given. The unique mechanical properties of a new material β-Ga2O3 formed on SiC layers grown on Si surfaces of orientations (100), (110) and (111) are described. [ABSTRACT FROM AUTHOR]

We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal–organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of β-Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the ( 2 ¯ 01) orientation peaks of β-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 × 1018 cm−3 and mobility of ~770 cm2V−1s−1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance–voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 × 1013 cm−2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV−1. A significant reduction in leakage current from ~10−4 A/cm2 for HFET to ~10−6 A/cm2 for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices. [ABSTRACT FROM AUTHOR]

In this study, GaxOyNz films were deposited onto p-Si (100) substrates by using electrodeposition technique under illumination. A mixture of gallium nitrate, ammonnium nitrade and distilled water was utilized as electrolyte. Platinum and p-Si were used as anode and cathode, respectively. After the deposition process of GaxOyNz/p-Si structure, temperature dependent Current-Voltage (I-V) measurements were performed and characterized between 20 °C and 100 °C in 10 °C steps to analyses of two dimensional density of interface states of the device. Characteristics show that GaxOyNz/p-Si device structure exhibits rectification behavior. [ABSTRACT FROM AUTHOR]

We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal–organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of β-Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the (2¯01) orientation peaks of β-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 × 1018 cm−3 and mobility of ~770 cm2V−1s−1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance–voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 × 1013 cm−2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV−1. A significant reduction in leakage current from ~10−4 A/cm2 for HFET to ~10−6 A/cm2 for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices.

Gallium oxide (Ga2O3) has emerged as a fourth-generation semiconductor for futuristic device requirements. Integration of Ga2O3 with industry-viable gallium nitride (GaN) can provide a pathway to design efficient device technology. In this paper, we design Ga2O3/GaN heterointerface by using a simple thermal annealing method under an oxygen-rich environment. Thermal annealing at 850 °C for 5 h results in a good yield of Ga2O3 from surficial GaN which was grown on sapphire and Si substrates. Surface morphology revealed a nanorod structure-based Ga2O3 on the GaN surface grown on industrial compatible Si substrate. XPS measurements provide a quantitative understanding of the heterostructure, where 84.62% and 70.92% of surficial GaN is converted into Ga2O3. Besides, the valence band maximum is shifted to a higher energy side in comparison to bare GaN samples. This helps in understanding the device physics of the grown heterostructures. Current-Voltage (I–V) characteristics revealed Schottky behaviour where the Schottky barrier height is increased after thermal annealing of the GaN films. Temperature correlated I–V characteristics suggest that the thermally annealed GaN films are stable up to 300 °C. These material structures can potentially be used in the high-temperature applications for power devices, optoelectronics, and sensing applications.

Wide bandgap semiconductors are ideal materials for the application of high power density, high frequency and low- loss power electronic devices, owning to the advantages of wide bandgap, high electron saturation velocity, and high breakdown field. Attributed to the high thermal conductivity, high chemical stability and high heat resistance of silicon carbide (SiC), epitaxy of wide bandgap semiconductors on SiC is promising to exploit the advantages of wide bandgap semiconductors and improve the performance of wide bandgap semiconductor devices. Benefiting from the continuous quality-improvement and cost-reduction of SiC substrates, wide bandgap semiconductors grown on SiC substrates are ushering in an explosive growth. Epitaxy of high quality wide bandgap semiconductors on SiC substrates is critical to the performance and reliability of wide bandgap semiconductor devices. This paper summarizes the recent progress obtained on epitaxial growth of SiC, gallium nitride (GaN) and gallium oxide (Ga2O3) on SiC substrates. In addition, the prospective of wide bandgap semiconductors grown on SiC substrates for high-performance electronics are prospected. [ABSTRACT FROM AUTHOR]

A new device structure, which includes a Ga2O3 current blocking layer (CBL) and a Ga2O3 surface passivation layer (SPL), is used to fabricate a GaN-based light-emitting diode (LED). Due to the inherent properties of Ga2O3 material, the current spreading phenomenon can be effectively improved and the surface leakage current and Fresnel reflection can be remarkably reduced. The appropriate thicknesses of the Ga2O3 CBL and SPL, according to the results from series experiments, are 10 and 50 nm, respectively. In an experiment, under an injection current density of 100 A/cm2, the studied LED device with a 10 nm-thick Ga2O3 CBL and a 50 nm-thick Ga2O3 SPL shows enhancements of 76.8%, 60.7%, 76.8%, and 56.2% in light output power (LOP), luminous efficacy, external quantum efficiency (EQE), and wall-plug efficiency, respectively, in comparison to a conventional LED without the designed structure. In addition, the studied LED exhibits obvious improvement in far-field radiation pattern compared to the conventional LED device. Thus, the studied structure, which includes an appropriate Ga2O3 CBL and SPL, offers a promising route to fabricate high-performance GaN-based LEDs. [ABSTRACT FROM AUTHOR]

The formation of GaN nanocrystals in SiO 2 /Si and SiN x /Si dielectric layers implanted with Ga + and N + ions, followed by annealing at 950 °C for 60–120 min in N 2, has been studied by high resolution transmission electron microscopy (HRTEM), synchrotron radiation X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) technique at the Ga K-edge, as well as by Rutherford Backscattering spectrometry (RBS), X-Ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS) and Scanning electron microscopy (SEM). The effect of the dielectric matrix, of the gas annealing environment (N 2) and of the annealing time at 950 °C have been investigated. GaN nanocrystals implanted near the surface are observed in SiO 2 /Si only. The hexagonal wurtzite crystalline structure was confirmed by HRTEM, XRD and Raman spectroscopy. However, the synthesis process is multiphasic as elemental Ga0 nanoparticles at larger depths and Ga 2 O 3 rods (~200–300 nm) on the surface were formed in addition to implanted h-GaN, as shown by TEM, XAFS, SEM, XPS and Raman spectroscopy. Moreover, Ga atoms are always remaining on some vacant Si sites in the SiO 2 matrix. The local environment around Ga is quite different in the SiN x matrix, as seen by XAFS. This difference can be explained by the gallium and nitrogen diffusions which are much faster in the case of the SiO 2 matrix, as shown by RBS profiles. Results are discussed in close comparison with existing literature. [ABSTRACT FROM AUTHOR]

This work presents the electrostatic analysis of a novel Ga2O3 vertical Schottky diode with three different guard ring (GR) configurations to reduce the peak electric field at the metal edges. Highly doped p-type GaN, p-type nonpolar AlGaN, and polarization-doped graded p-AlGaN are simulated and analyzed as the GR material, which forms a heterojunction with the Ga2O3 drift layer. GR with nonpolar graded p-AlGaN with a bandgap larger than Ga2O3 is found to show the best performance in terms of screening the electric field at the metal edges. The proposed GR configuration is also compared with a reported Ga2O3 Schottky diode with no GR and a structure with high-resistive nitrogen-doped GR. The optimized design is predicted to have a breakdown voltage as high as 6.2 kV and a specific ON-resistance of 3.55m Ω-cm2, which leads to an excellent power figure of merit of 10.8 GW/cm2. [ABSTRACT FROM AUTHOR]

Featured Application: GaN/Ga2O3 core/shell nanowires appear as promising solution to fabricate gas sensors working in a large range of temperature, from ambient temperature to high temperatures. Thanks to their core-shell heterostructures, these systems are based on the NW resistance modulation process, then offering the possibility to improve the sensor performances. The development of sensors working in a large range of temperature is of crucial importance in areas such as monitoring of industrial processes or personal tracking using smart objects. Devices integrating GaN/Ga2O3 core/shell nanowires (NWs) are a promising solution for monitoring carbon monoxide (CO). Because the performances of sensors primarily depend on the material properties composing the active layer of the device, it is essential to control them and achieve material synthesis in the first time. In this work, we investigate the synthesis of GaN/Ga2O3 core-shell NWs with a special focus on the formation of the shell. The GaN NWs grown by plasma-assisted molecular beam epitaxy, are post-treated following thermal oxidation to form a Ga2O3-shell surrounding the GaN-core. We establish that the shell thickness can be modulated from 1 to 14 nm by changing the oxidation conditions and follows classical oxidation process: A first rapid oxide-shell growth, followed by a reduced but continuous oxide growth. We also discuss the impact of the atmosphere on the oxidation growth rate. By combining XRD-STEM and EDX analyses, we demonstrate that the oxide-shell is crystalline, presents the β-Ga2O3 phase, and is synthesized in an epitaxial relationship with the GaN-core. [ABSTRACT FROM AUTHOR]

The development of sensors working in a large range of temperature is of crucial importance in areas such as monitoring of industrial processes or personal tracking using smart objects. Devices integrating GaN/Ga2O3 core/shell nanowires (NWs) are a promising solution for monitoring carbon monoxide (CO). Because the performances of sensors primarily depend on the material properties composing the active layer of the device, it is essential to control them and achieve material synthesis in the first time. In this work, we investigate the synthesis of GaN/Ga2O3 core-shell NWs with a special focus on the formation of the shell. The GaN NWs grown by plasma-assisted molecular beam epitaxy, are post-treated following thermal oxidation to form a Ga2O3-shell surrounding the GaN-core. We establish that the shell thickness can be modulated from 1 to 14 nm by changing the oxidation conditions and follows classical oxidation process: A first rapid oxide-shell growth, followed by a reduced but continuous oxide growth. We also discuss the impact of the atmosphere on the oxidation growth rate. By combining XRD-STEM and EDX analyses, we demonstrate that the oxide-shell is crystalline, presents the β-Ga2O3 phase, and is synthesized in an epitaxial relationship with the GaN-core.

Gallium oxide (Ga 2 O 3) has attracted much attention for its ultra-wide band gap and superior optoelectronic properties in the field of ultraviolet (UV) photodetectors. However, Ga 2 O 3 -based photodetectors still face problems such as slow response speed, large dark current and high power consumption. In this work, we design an n-Ga 2 O 3 /p-GaN vertical heterojunction in a transverse device and use it to construct a high-performance UV photodetector. The GaN film directly connects to the electrodes, while the Ga 2 O 3 nanowires cover the top surface of the GaN and do not contact with any electrode. Based on this unique heterostructure, the photodetector demonstrates a low dark current and fast photoresponse speed under 254 nm irradiation. On the other hand, the photodetector can be operated at 0 V bias due to asymmetric Schottky barriers caused by the difference in electrode size. The photoresponse, specific detectivity and photoresponse speed of the photodetector are calculated to be 44.98 mA/W, 5.33 × 1011 Jones and 383 ms, respectively, under self-powered mode. The enhanced UV photoresponse and self-powered mechanism of the photodetector are discussed in detail via the schematic diagrams of energy band structure and carrier transport process. At last, a vivid image is obtained using the Ga 2 O 3 /GaN photodetector as an imaging pixel in the imaging system. This work provides an effective strategy to construct high-performance UV photodetectors toward optical imaging. [Display omitted] • A Ga 2 O 3 /GaN vertical heterostructure in a transverse photodetector is constructed. • The photodetector shows a fast photoresponse speed and high photoresponsivity. • The photodetector can be operated at 0 V bias due to asymmetric Schottky barrier height. • The enhanced UV photoresponse and self-powered mechanism of the photodetector are discussed in detail. • A vivid image is obtained using the Ga 2 O 3 /GaN photodetector as an imaging pixel in the imaging system. [ABSTRACT FROM AUTHOR]

Six out of seven crystal systems are optically anisotropic and birefringent. We review recent insight that biaxial crystals generally exhibit four singular axes (or exceptional points) which can pairwise degenerate for special cases. Planar anisotropic microcavities are discussed as effectively biaxial systems and we predict exceptional points and demonstrate experimentally partially coalesced eigenstates. Also the general form of the dielectric function of anisotropic crystals based on individual dipole oscillators for phonon and electronic resonance is discussed. The impact of birefringence on Raman scattering intensities has been historically either ignored or modeled incorrectly. A recent theory for uniaxial and biaxial crystals explains experimental Raman scattering intensities for excitation off the principal directions without free parameters, allowing the unambiguous determination of the Raman tensor components. The above points are demonstrated and relevant in particular for the currently technologically important materials GaN, ZnO (uniaxial) and β‐Ga2O3 (biaxial). Formula for the Raman scattering intensity as a function of incoming and outgoing polarization and the Raman tensor viewed through birefringent crystal (calcite). Invited Review@RRL on the occasion of 10th anniversary of pss RRL: The anisotropic optics (novel theory of Raman scattering off the principal axes) and the singular optics (spectral dispersion of Windungsachsen from generalized ellipsometry) in monoclinic gallia are reviewed. The latter represent exceptional points, a property of complex symmetric matrices, and are predicted to also exist in anisotropic microcavities leading to circularly polarized eigenstates. [ABSTRACT FROM AUTHOR]

Patterned gallium oxide (Ga2O3) using one-step patterning followed by oxygen plasma treatment on a p-GaN layer can function as both current-blocking and optical-scattering regions for uniform current spreading and improved light-extraction efficiencies. The results showed that the optical output power of the LED with patterned Ga2O3 increased by 16.8% at 60 mA compared to that of conventional LEDs. Numerical studies on light tracing and emission pattern, and external quantum efficiency evaluation support the improvement of both uniform current spreading and light-extraction efficiencies by patterned Ga2O3. [ABSTRACT FROM AUTHOR]

A β-Ga2O3 thin film was formed on a (0001) c-plane GaN template substrate by gallium evaporation in an oxygen plasma. From X-ray diffraction measurements using ω-2 θ and ϕ scans, the film orientation was found to be ( [ABSTRACT FROM AUTHOR]

In this article, β-Ga 2 O 3 /GaN-based solar-blind phototransistors are fabricated using a thermal oxidation process performed on the p-GaN layer of a p-GaN/n-GaN junction to form the β-Ga 2 O 3 /p-GaN/n-GaN heterostructure. The thermal-oxidized β-Ga 2 O 3 films exhibit a ( 2 ̅ 01) -orientated crystal phase and high-resistivity property. The high-resistivity β-Ga 2 O 3 layer can be converted into an n-type β-Ga 2 O 3 layer through Si ion implantation and a subsequent thermal annealing process. The typical electron concentration and mobility of the Si-implanted β-Ga 2 O 3 are as high as 3.2 × 1020 cm−3 and 177 cm2v−1s−1, respectively. The n-type β-Ga 2 O 3 and unimplanted β-Ga 2 O 3 layers serve as the collector associating with the p-GaN and n-GaN layers, which function as the base and emitter, respectively, to construct the heterojunction phototransistors (HPTs). The HPTs exhibit a distinct cut-off wavelength at around 260 nm, indicating that the photocurrents result from the β-Ga 2 O 3 layers rather than the p-GaN and n-GaN layers. The HPTs also show a significant bias-dependent responsivity in the deep UV (λ < 260 nm) region. This increased responsivity can be attributed to band discontinuity, resulting in the accumulation of photogenerated carriers at the β-Ga 2 O 3 /p-GaN interface. The preliminary results suggest that the β-Ga 2 O 3 /GaN-based HPTs can be achieved through the thermal oxidation of a p-GaN/n-GaN epitaxial structure. [Display omitted] • β-Ga 2 O 3 /GaN-based solar-blind phototransistors are fabricated by oxidation process. • A β-Ga 2 O 3 /p-GaN/n-GaN heterostructure formed on a p-GaN/n-GaN junction. • The phototransistors show a bias-dependent responsivity in the λ < 260 nm region. • High-resistivity Ga 2 O 3 is converted into n-type conduction via Si ion implantation. [ABSTRACT FROM AUTHOR]

High-performance ultraviolet (UV) photodetector was fabricated based on amorphous Ga 2 O 3 /ZnO nanoarrays(NRs) on p-GaN film. The obtained detector displays excellent UV sensing properties which covers UV-A/UV-C region with fast response without external bias. The high photosensitivity can be ascribed to the geometry of the match-like Ga 2 O 3 /ZnO NRs and emergence of the built-in field between the amorphous Ga 2 O 3 and ZnO interface. The results will provide a new method to improve the ZnO/GaN heterostructure for applications in broadband ultraviolet sensing. High-performance ultraviolet (UV) photodetector was fabricated based on amorphous Ga 2 O 3 /ZnO nanoarrays(NRs) on p-GaN film. The obtained detector displays excellent UV sensing properties which covers UV-A/UV-C region with fast response without external bias. The high photosensitivity can be ascribed to the geometry of the match-like Ga 2 O 3 /ZnO NRs and emergence of the built-in field between the amorphous Ga 2 O 3 and ZnO interface. The results will provide a new method to improve the ZnO/GaN heterostructure for applications in broadband ultraviolet sensing. [Display omitted] • Amorphous Ga2O3/ZnO NRs/GaN photodetector were fabricated by combining aqueous method and sputtering method. • The ZnO/GaN response performance is improved by depositing amorphous Ga2O3 layer. • The device has an excellent response in the ultraviolet A and ultraviolet C regions without external bias. [ABSTRACT FROM AUTHOR]

The mechanisms of ion-induced defect formation and physical characteristics promoting radiation tolerance of wide and ultra-wide bandgap semiconductors are not well-studied and understood. In contrast to gallium nitride (GaN), gallium oxide (Ga 2 O 3) can be crystallized in several polymorphs having different crystal structures and physical properties. In the preset paper, the damage buildup in wurtzite GaN as well as in corundum (α -) and monoclinic (β -) Ga 2 O 3 polymorphs bombarded at room temperature with 40 keV P+ ions is studied by Rutherford backscattering/channeling spectrometry. We demonstrate that ion-beam-induced damage formation in Ga 2 O 3 is different from that observed in GaN and dramatically depends on the polymorph type. Both Ga 2 O 3 polymorphs cannot be rendered amorphous and exhibit considerably higher damage saturation at ∼90% of the full amorphization as compared to that of GaN. Intriguing enough the metastable α -Ga 2 O 3 demonstrates considerably higher radiation resistance as compared to the most thermodynamically stable β -Ga 2 O 3 polymorph. Furthermore, our results indicate that the sample surface and dynamic annealing play a significant role in the ion-induced damage formation processes in all Ga-based compounds studied. • Kinetics of ion irradiation damage accumulation in α- and β-Ga 2 O 3 and GaN is studied. • α -Ga 2 O 3 is more susceptible to radiation damage than GaN. • α -Ga 2 O 3 is considerably higher radiation resistant then the stable β -Ga 2 O 3. • Mechanisms of radiation damage formation in the α - and β -Ga 2 O 3 are different. [ABSTRACT FROM AUTHOR]

Abstract: High-quality gallium nitride (GaN) nanowires (NWs) were successfully synthesized in two steps without the aid of any foreign catalyst. Initially, Ga2O3 nanobelts (NBs) were grown on sapphire substrates via the thermal evaporation of GaN at 1150°C. The NBs exhibited clear peaks in the X-ray diffraction spectrum corresponding to the monoclinic β-Ga2O3. Nitridation at 1000°C efficiently converted β-Ga2O3 into one-dimensional GaN NWs. X-ray diffraction analysis confirmed the synthesized nanowires of GaN with hexagonal wurtzite-type crystal structure. Field emission scanning electron microscopy (FESEM) observations revealed that the grown nanowires have a curvature shape with diameters ranging from 30 to 160nm and lengths up to several micrometers. Photoluminescence studies of GaN NWs showed the presence of a band edge emission is near 3.306eV and a red luminescence peak at 1.87eV. Raman scattering analysis reveals that GaN NWs have vibrational modes. The kinetics of nitridation from β-Ga2O3 NBs to wurtzite GaN NWs in an NH3 atmosphere is also presented. [Copyright &y& Elsevier]

We present first-principle calculations on the heterojunction between a wurtzite GaN(0001) film and a monoclinic β-Ga2O3(100) substrate. The relative stability of different models of the GaN(0001)/Ga2O3(100) interface was investigated and the most favorable interface consists of threefold- and sixfold-coordinated Ga. This interface structure gives rise to Ga-polarity in the GaN(0001) epitaxial film. A detailed analysis of the electronic structure indicates that undistorted bonding at the interface stabilizes this structure between a wurtzite GaN(0001) and a monoclinic β-Ga2O3(100). [ABSTRACT FROM AUTHOR]

By using a He-Cd laser in a chemical solution of H3PO4 with a pH value of 3.5, Ga oxide films were directly grown on n-type GaN. From the energy-dispersive spectrometer (EDS) measurement and x-ray diffraction (XRD) measurement, the grown Ga oxide film was identified as (104) α-Ga2O3 structure. A small amount of phosphors existed and bonded with oxygen on the grown films. The as-grown films were amorphous. From the XRD analysis, it is evident that annealing of the α-Ga2O3 films led to a change in the microstructure from an amorphous to a polycrystalline phase. In addition, the as-grown low-density films gradually became dense films during the annealing process. Furthermore, the surface roughness of the annealed films also gradually decreased. Hexagonal pinholes on the grown films were observed. The density of the hexagonal pinholes was similar to the defect density of the n-type GaN. From the cross-sectional transmission electron microscopy (TEM) micrographs, it is evident that the hexagonal pinholes originated from defects in the n-type GaN. [ABSTRACT FROM AUTHOR]

Gallium nitride–gallium oxide structures were formed by heat-treating gallium nitride (GaN) powders in several gas environments at temperatures from 400°C to 900°C. The platelet nanostructured particles were examined at several stages of oxidation by microscopic, structural, chemical and optical spectroscopic techniques. Particle morphology, nanophase characterization and photoluminescence data showed that the oxide layers passivate the GaN platelets surfaces and significantly reduce the yellow emission while enhancing near band-edge emission. [Copyright &y& Elsevier]

Measuring the band gap of bulk materials by valence electron energy loss spectroscopy (VEELS) is not straightforward. Mathematical procedures used to recover the single scattering distribution from raw data introduce artefacts in the signal, which complicate the gap measurement. In this work, we propose a method to overcome this and measure the direct band gap energy with an accuracy of ±0.1 eV. The method is tested on six crystalline wide-band gap materials: MgO, Ga2O3, SrTiO3, ZnO, BN and GaN. [Copyright &y& Elsevier]

High quality gallium nitride thin films have been successfully grown on the Ga-diffused Si(1 1 1) substrates through ammoniating Ga2O3 thin films deposited by r.f. magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscope (AFM) and photoluminescence (PL) were used to characterize the synthesized samples. The analyses reveal that the formed films are high quality polycrystalline hexagonal gallium nitride. The as-formed GaN films show a flat surface topography with RMS roughness varied from 29 to 48 A˚. The strong near-band-edge-emission peak around 368 nm was observed at room temperature. This is a novel method to fabricate GaN thin films based on the direct reaction between Ga2O3 and NH3 on the Ga-diffused Si(1 1 1) substrates. [Copyright &y& Elsevier]

• Ga 2 O 3 films were deposited on a-, m- and r-plane sapphire and epi-GaN substrates. • ε-Ga 2 O 3 films grown along the (0001) crystal plane family were obtained. • Ga 2 O 3 films deposited on different substrates had very different surface morphologies. • Absorption spectrum and XRD diffraction of Ga 2 O 3 film were investigated. Ga 2 O 3 films were deposited on non-polar sapphire and epi-GaN substrates at low temperature by MOCVD. The ε-Ga 2 O 3 films, which were preferentially grown along the (0001) crystal plane family, were obtained on a-, r-plane sapphire and GaN substrates, and contained a certain polycrystalline component. On the m-plane sapphire substrate, a polycrystalline film containing α/β-Ga 2 O 3 was obtained. The grain size and surface fluctuations on m-plane sapphire substrate were large, while the film on r-plane sapphire and GaN substrates had more uniform surface and the film on GaN substrate had the flattest surface. Optical analysis indicated that the best quality Ga 2 O 3 film on these sapphire substrates was deposited on r-plane substrate. XRD showed that the Ga 2 O 3 film on GaN substrate had better crystalline quality than that on a-plane sapphire substrate. [ABSTRACT FROM AUTHOR]

• Wet-chemically cleaned GaN(0001) surface was investigated by CAICISS. • Oxygen is adsorbed at on-top sites on GaN(0001) surface. • The Ga–O bond distance was estimated to be between 1.80 and 1.85 Å. • The bond distance is consistent with the Ga–O tetrahedral bond distance in β -Ga 2 O 3. Oxygen adsorption on wet-chemically cleaned GaN(0001) surface has been studied by coaxial impact collision ion scattering spectroscopy (CAICISS). The intensity variation of time-of-flight spectra obtained by CAICISS was compared with simulation results. The CAICISS analysis showed that oxygen is adsorbed at the top of Ga atoms at the surface. The Ga–O bond distance was estimated to be between 1.80 and 1.85 Å. The estimated bond distance is consistent with the Ga–O tetrahedral bond distance in β -Ga 2 O 3. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ga 2 O 3 nitridation with NH 3 to GaN occurs via amorphous gallium oxynitrides intermediates. • NH 3 adsorption was barrier less in which N is attracted towards gallium (Ga–N). • Two limiting steps: (1) N–H dissociation from the first NH 2 * to NH* and (2) last H 2 O release. • Pore diffusion influence the GaN formation at high temperatures and high conversions. TG experiments and DFT calculations were used to investigate the mechanism of gallium oxide nitridation to gallium nitride. The overall conversion of the gas-solid reaction can be best described by a modified integrated model that accounts for diffusion influence at high temperatures and conversions. For that model, an apparent activation energy of 154 kJ mol−1 and a reaction order for Ga 2 O 3 of n = 0.36 were estimated. NH 3 favorably adsorbed on Ga 2 O 3 without any energy barrier in which the nitrogen is attracted towards gallium (Ga–N). The Ga 2 O 3 surface was nitridated to GaN via adsorbed NH 2 *, NH* and H* intermediates, obtained through NH 3 * dissociation, increasingly stabilized by the surface, preventing their early desorption, and testifying of the positive nitrogen (N) atom insertion into the crystal. The N–H bond became harder to break, increasing the dissociation reaction and activation energies. The first NH 2 * dissociation to NH* was a limiting step, with a high activation energy of 2.81 eV. The second limiting step was the formation of the third H 2 O molecule with an activation energy of 3.07 eV. According to the observations, the first layer of GaN was organized towards the wurtzite crystal structure. [ABSTRACT FROM AUTHOR]

In this paper,β-Ga 2 O 3 films were grown on epi-GaN/sapphire (0001) substrates at 600,700 and 800 °C by low pressure MOCVD, respectively.And the influences of temperature on the crystal structure, surface morphology and element chemical state were investigated.XRD analysis found that β-Ga 2 O 3 films were preferentially grown along the (−201) crystal plane, and crystal quality of the films improved with increasing temperature.AFM and SEM indicated that the surface morphology of films was obviously changed with the increasing temperature, and the surface became compact and flat.The FWHM value of XRD rocking curve at 800 °C less than those grown at 600 and 700 °C, indicating that the β-Ga 2 O 3 film grown at 800 °C has better crystal quality.XPS showed that the intensity of the Ga 2p, Ga 3d and O 1s peaks increased with temperature, and epitaxial relationship of β-Ga 2 O 3 was confirmed by HRTEM, consistent with the XRD results. • β-Ga 2 O 3 films were grown on epi-GaN/sapphire (0001) substrates by low-pressure MOCVD. • β-Ga 2 O 3 films wwere preferentially grown along the (−201) direction. • The surface morphology and crystal quality changed significantly with increasing temperature. • XPS indicated that the intensity of the Ga 2p, Ga 3d and O 1s peaks increased with increasing temperature. • The Raman analysis detected low-frequency and intermediate-frequency Raman vibration mode of β-Ga 2 O 3. [ABSTRACT FROM AUTHOR]

In this paper, vertically aligned GaN@Ga 2 O 3 core-shell heterostructured nanowire arrays have been fabricated by thermal oxidation of GaN nanowire arrays. GaN nanowire arrays have been prepared by inductively coupled plasma etching. The GaN@Ga 2 O 3 nanowire arrays have the good morphology and the thickness of the Ga 2 O 3 shell can be controlled by the oxidation duration and temperature. The photocatalytic activity of vertically aligned GaN@Ga 2 O 3 nanowires has been first evaluated by the degradation of Rhodamine B solution. Compared with the original GaN nanowires and the oxidized Ga 2 O 3 nanowires, GaN@Ga 2 O 3 nanowires exhibit superior photocatalytic activity. This finding suggests that GaN nanowire arrays with enhanced photocatalytic activity could be obtained by construct heterostructured GaN-based nanocomposite, which provides a new possibility for photocatalytic applications. Vertically aligned GaN@Ga 2 O 3 NAs have been fabricated by thermally oxidizing GaN NAs and the core-shell NAs exhibited enhanced photodegradation rate of Rhodamine B. Image 1 • Vertically aligned GaN@Ga 2 O 3 NAs have been obtained by thermally oxidizing GaN NAs. • The Ga 2 O 3 shell thickness can be controlled by oxidizing temperature and time. • The core-shell NAs showed the best photodegradation efficiency of Rhodamine B. [ABSTRACT FROM AUTHOR]

Abstract: The thermal techniques including thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were employed to investigate the thermal oxidation behaviors of gallium nitride (GaN) in the environment of open air. It was found that the thermal oxidation behaviors of GaN powders followed the two-step reaction being exothermic. Formation of Ga–O islands on the surface of GaN was found in the temperature range between 200 and 680 °C by FTIR and XRD patterns. The gallium oxide (Ga2O3) was gradually formed in the interior of GaN when the thermal temperature exceeded 810 °C. Over 915 °C, GaN was all converted into β-Ga2O3 observed by FTIR and XRD patterns. [Copyright &y& Elsevier]

In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga2O3 layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga2O3-air layers, by a rough Ga2O3 surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. [ABSTRACT FROM PUBLISHER]