In this work, we reported a high-performance-based ultraviolet-visible (UV-VIS) photodetector based on a TiO₂@GaO_xN_y-Ag heterostructure. Ag particles were introduced into TiO₂@GaO_xN_y to enhance the visible light detection performance of the heterojunction device. At 380 nm, the responsivity and detectivity of TiO₂@GaO_xN_y-Ag were 0.94 A/W and 4.79 × 10⁹ Jones, respectively, and they increased to 2.86 A/W and 7.96 × 10¹⁰ Jones at 580 nm. The rise and fall times of the response were 0.19/0.23 and 0.50/0.57 s, respectively. Uniquely, at 580 nm, the responsivity of fabricated devices is one to four orders of magnitude higher than that of the photodetectors based on TiO₂, Ga₂O₃, and other heterojunctions. The excellent optoelectronic characteristics of the TiO₂@GaO_xN_y-Ag heterojunction device could be mainly attributed to the synergistic effect of the type-Ⅱ band structure of the metal–semiconductor–metal heterojunction and the plasmon resonance effect of Ag, which not only effectively promotes the separation of photogenerated carriers but also reduces the recombination rate. It is further illuminated by finite difference time domain method (FDTD) simulation and photoelectric measurements. The TiO₂@GaO_xN_y-Ag arrays with high-efficiency detection are suitable candidates for applications in energy-saving communication, imaging, and sensing networks.

Homoepitaxial growth of Si-doped β-Ga₂O₃ films on semi-insulating (100) β-Ga₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga₂O₃ films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga₂O₃ film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 10¹⁵ – 1.74 × 10²⁰ cm⁻³. Hall measurements demonstrate a high electron mobility value of 51 cm²/(V·s), corresponding to a carrier concentration of 7.19 × 10¹⁸ cm⁻³ and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10^-4 Ω·cm² for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 10¹⁹ cm⁻³, confirming the effective Si doing in the MOCVD epitaxy.

Sn doping is an effective way to improve the response rate of Ga₂O₃ film based solar-blind detectors. In this paper, Sn-doped Ga₂O₃ films were prepared on a sapphire substrate by radio frequency magnetron sputtering. The films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet visible spectroscopy, and the effect of annealing atmosphere on the properties of films was studied. The Ga₂O₃ films changed from amorphous to β-Ga₂O₃ after annealing at 900 °C. The films were composed of micro crystalline particles with a diameter of about 5–20 nm. The β-Ga₂O₃ had high transmittance for wavelengths above 300 nm, and obvious absorption for solar-blind signals at 200–280 nm. The metal semiconductor metal type solar-blind detectors were prepared. The detector based on Sn-doped β-Ga₂O₃ thin film annealed in N₂ has the best response performance to 254 nm light. The photo-current is 10 μA at 20 V, the dark-current is 5.76 pA, the photo dark current ratio is 1.7 × 10⁶, the response rate is 12.47 A/W, the external quantum efficiency is 6.09 × 10³%, the specific detection rate is 2.61 × 10¹² Jones, the response time and recovery time are 378 and 90 ms, respectively.

High thickness uniformity and large-scale films of α-Ga₂O₃ are crucial factors for the development of power devices. In this work, a high-quality 2-inch α-Ga₂O₃ epitaxial film on c-plane sapphire substrates was prepared by the mist-CVD method. The growth rate and phase control mechanisms were systematically investigated. The growth rate of the α-Ga₂O₃ films was limited by the evaporation of the microdroplets containing gallium acetylacetonate. By adjusting the substrate position (z) from 80 to 50 mm, the growth rate was increased from 307 nm/h to 1.45 μm/h when the growth temperature was fixed at 520 °C. When the growth temperature exceeded 560 °C, ε-Ga₂O₃ was observed to form at the edges of 2-inch sapphire substrate. Phase control was achieved by adjusting the growth temperature. When the growth temperature was 540 °C and the substrate position was 50 mm, the full-width at half maximum (FWHM) of the rocking curves for the (0006) and (10-14) planes were 0.023° and 1.17°. The screw and edge dislocations were 2.3 × 10⁶ and 3.9 × 10¹⁰ cm^-2, respectively. Furthermore, the bandgaps and optical transmittance of α-Ga₂O₃ films grown under different conditions were characterized utilizing UV-visible and near-IR scanning spectra.

We investigated the influence of the growth temperature, O₂ flow, molar ratio between Ga₂O₃ powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire (0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga₂O₃ illustrate that β-Ga₂O₃ growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga₂O₃ films was produced when the O₂ flow was 20 sccm. To guarantee that β-Ga₂O₃ films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga₂O₃ powder should be set at 10 : 1.

Beta gallium oxide (β-Ga₂O₃) has attracted significant attention for applications in power electronics due to its ultra-wide bandgap of ~ 4.8 eV and the large critical electric field of 8 MV/cm. These properties yield a high Baliga’s figures of merit (BFOM) of more than 3000. Though β-Ga₂O₃ possesses superior material properties, the lack of p-type doping is the main obstacle that hinders the development of β-Ga₂O₃-based power devices for commercial use. Constructing heterojunctions by employing other p-type materials has been proven to be a feasible solution to this issue. Nickel oxide (NiO) is the most promising candidate due to its wide band gap of 3.6–4.0 eV. So far, remarkable progress has been made in NiO/β-Ga₂O₃ heterojunction power devices. This review aims to summarize recent advances in the construction, characterization, and device performance of the NiO/β-Ga₂O₃ heterojunction power devices. The crystallinity, band structure, and carrier transport property of the sputtered NiO/β-Ga₂O₃ heterojunctions are discussed. Various device architectures, including the NiO/β-Ga₂O₃ heterojunction pn diodes (HJDs), junction barrier Schottky (JBS) diodes, and junction field effect transistors (JFET), as well as the edge terminations and super-junctions based on the NiO/β-Ga₂O₃ heterojunction, are described.

Power electronic devices are of great importance in modern society. After decades of development, Si power devices have approached their material limits with only incremental improvements and large conversion losses. As the demand for electronic components with high efficiency dramatically increasing, new materials are needed for power device fabrication. Beta-phase gallium oxide, an ultra-wide bandgap semiconductor, has been considered as a promising candidate, and various β-Ga₂O₃ power devices with high breakdown voltages have been demonstrated. However, the realization of enhancement-mode (E-mode) β-Ga₂O₃ field-effect transistors (FETs) is still challenging, which is a critical problem for a myriad of power electronic applications. Recently, researchers have made some progress on E-mode β-Ga₂O₃ FETs via various methods, and several novel structures have been fabricated. This article gives a review of the material growth, devices and properties of these E-mode β-Ga₂O₃ FETs. The key challenges and future directions in E-mode β-Ga₂O₃ FETs are also discussed.

This study explores the epitaxial relationship and electrical properties of α-Ga₂O₃ thin films deposited on a-plane, m-plane, and r-plane sapphire substrates. We characterize the thin films by X-ray diffraction and Raman spectroscopy, and elucidate thin film epitaxial relationships with the underlying sapphire substrates. The oxygen vacancy concentration of α-Ga₂O₃ thin films on m-plane and r-plane sapphire substrates are higher than α-Ga₂O₃ thin film on a-plane sapphire substrates. All three thin films have a high transmission of over 80% in the visible and near-ultraviolet regions, and their optical bandgaps stay around 5.02–5.16 eV. Hall measurements show that the α-Ga₂O₃ thin film grown on r-plane sapphire has the highest conductivity of 2.71 S/cm, which is at least 90 times higher than the film on a-plane sapphire. A similar orientation-dependence is seen in their activation energy as revealed by temperature-dependent conductivity measurements, with 0.266, 0.079, and 0.075 eV for the film on a-, m-, r-plane, respectively. The origin of the distinct transport behavior of films on differently oriented substrates is suggested to relate with the distinct evolution of oxygen vacancies at differently oriented substrates. This study provides insights for the substrate selection when growing α-Ga₂O₃ films with tunable transport properties.

Output power and reliability are the most important characteristic parameters of semiconductor lasers. However, catastrophic optical damage (COD), which usually occurs on the cavity surface, will seriously damage the further improvement of the output power and affect the reliability. To improve the anti-optical disaster ability of the cavity surface, a non-absorption window (NAW) is adopted for the 915 nm InGaAsP/GaAsP single-quantum well semiconductor laser using quantum well mixing (QWI) induced by impurity-free vacancy. Both the principle and the process of point defect diffusion are described in detail in this paper. We also studied the effects of annealing temperature, annealing time, and the thickness of SiO₂ film on the quantum well mixing in a semiconductor laser with a primary epitaxial structure, which is distinct from the previous structures. We found that when compared with the complete epitaxial structure, the blue shift of the semiconductor laser with the primary epitaxial structure is larger under the same conditions. To obtain the appropriate blue shift window, the primary epitaxial structure can use a lower annealing temperature and shorter annealing time. In addition, the process is less expensive. We also provide references for upcoming device fabrication.

Ultrawide band gap semiconductors are promising solar-blind ultraviolet (UV) photodetector materials due to their suitable bandgap, strong absorption and high sensitivity. Here, β-Ga₂O₃ microwires with high crystal quality and large size were grown by the chemical vapor deposition (CVD) method. The microwires reach up to 1 cm in length and were single crystalline with low defect density. Owing to its high crystal quality, a metal–semiconductor–metal photodetector fabricated from a Ga₂O₃ microwire showed a responsivity of 1.2 A/W at 240 nm with an ultrahigh UV/visible rejection ratio (R_peak/R_{400 nm}) of 5.8 × 10⁵, indicating that the device has excellent spectral selectivity. In addition, no obvious persistent photoconductivity was observed in the test. The rise and decay time constants of the device were 0.13 and 0.14 s, respectively. This work not only provides a growth method for high-quality Ga₂O₃ microwires, but also demonstrates the excellent performance of Ga₂O₃ microwires in solar-blind ultraviolet detection.

The anisotropic properties and applications of β-gallium oxide (β-Ga₂O₃) are comprehensively reviewed. All the anisotropic properties are essentially resulted from the anisotropic crystal structure. The process flow of how to exfoliate nanoflakes from bulk material is introduced. Anisotropic optical properties, including optical bandgap, Raman and photoluminescence characters are comprehensively reviewed. Three measurement configurations of angle-resolved polarized Raman spectra (ARPRS) are reviewed, with Raman intensity formulas calculated with Raman tensor elements. The method to obtain the Raman tensor elements of phonon modes through experimental fitting is also introduced. In addition, the anisotropy in electron mobility and affinity are discussed. The applications, especially polarization photodetectors, based on β-Ga₂O₃ were summarized comprehensively. Three kinds of polarization detection mechanisms based on material dichroism, 1D morphology and metal-grids are discussed in-depth. This review paper provides a framework for anisotropic optical and electric properties of β-Ga₂O₃, as well as the applications based on these characters, and is expected to lead to a wider discussion on this topic.

In the era of accelerated development in artificial intelligence as well as explosive growth of information and data throughput, underlying hardware devices that can integrate perception and memory while simultaneously offering the benefits of low power consumption and high transmission rates are particularly valuable. Neuromorphic devices inspired by the human brain are considered to be one of the most promising successors to the efficient in-sensory process. In this paper, a homojunction-based multi-functional optoelectronic synapse (MFOS) is proposed and testified. It enables a series of basic electrical synaptic plasticity, including paired-pulse facilitation/depression (PPF/PPD) and long-term promotion/depression (LTP/LTD). In addition, the synaptic behaviors induced by electrical signals could be instead achieved through optical signals, where its sensitivity to optical frequency allows the MFOS to simulate high-pass filtering applications in situ and the perception capability integrated into memory endows it with the information acquisition and processing functions as a visual system. Meanwhile, the MFOS exhibits its performances of associative learning and logic gates following the illumination with two different wavelengths. As a result, the proposed MFOS offers a solution for the realization of intelligent visual system and bionic electronic eye, and will provide more diverse application scenarios for future neuromorphic computing.

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies. A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency (~THz). However, the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light. Here, we design a system that combines Ag nanocavity with GaAs/AlAs phononic superlattices, where phonons with the frequency of 4.2 THz can be confined in a pillar with ~4 nm diameter. The Q _c/V reaches 0.22 nm^-3, which is ~80 times that of the photonic crystal (PhC) nanobeam and ~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity, where Q­_c is optical quality factor and V is mode volume. The optomechanical single-photon coupling strength can reach 12 MHz, which is an order of magnitude larger than that of the PhC nanobeam. In addition, the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg, which is much smaller than the PhC nanobeam. The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics, quantum information, and terahertz-light transducer.

Recently, the two-dimensional (2D) form of Ruddlesden-Popper perovskite (RPP) has been widely studied. However, the synthesis of one-dimensional (1D) RPP is rarely reported. Here, we fabricated a photodetector based on RPP microwires (RPP-MWs) and compared it with a 2D-RPP photodetector. The results show that the RPP-MWs photodetector possesses a wider photoresponse range and higher responsivities of 233 A/W in the visible band and 30 A/W in the near-infrared (NIR) band. The analyses show that the synthesized RPP-MWs have a multi-layer, heterogeneous core-shell structure. This structure gives RPP-MWs a unique band structure, as well as abundant trap states and defect levels, which enable them to acquire better photoresponse performance. This configuration of RPP-MWs provides a new idea for the design and application of novel heterostructures.

Spin injection and detection in bulk GaN were investigated by performing magnetotransport measurements at low temperatures. A non-local four-terminal lateral spin valve device was fabricated with Co/GaN Schottky contacts. The spin injection efficiency of 21% was achieved at 1.7 K. It was confirmed that the thin Schottky barrier formed between the heavily n-doped GaN and Co was conducive to the direct spin tunneling, by reducing the spin scattering relaxation through the interface states.

Developing low-cost, efficient, and stable photocatalysts is one of the most promising methods for large-scale solar water splitting. As a metal-free semiconductor material with suitable band gap, graphitic carbon nitride (g-C₃N₄) has attracted attention in the field of photocatalysis, which is mainly attributed to its fascinating physicochemical and photoelectronic properties. However, several inherent limitations and shortcomings—involving high recombination rate of photocarriers, insufficient reaction kinetics, and optical absorption—impede the practical applicability of g-C₃N₄. As an effective strategy, vacancy defect engineering has been widely used for breaking through the current limitations, considering its ability to optimize the electronic structure and surface morphology of g-C₃N₄ to obtain the desired photocatalytic activity. This review summarizes the recent progress of vacancy defect engineered g-C₃N₄ for solar water splitting. The fundamentals of solar water splitting with g-C₃N₄ are discussed first. We then focus on the fabrication strategies and effect of vacancy generated in g-C₃N₄. The advances of vacancy-modified g-C₃N₄ photocatalysts toward solar water splitting are then discussed. Finally, the current challenges and future opportunities of vacancy-modified g-C₃N₄ are summarized. This review aims to provide a theoretical basis and guidance for future research on the design and development of highly efficient defective g-C₃N₄.

Antimony selenide (Sb₂Se₃) is an emerging solar cell material. Here, we demonstrate that an organic small molecule of 4, 4', 4''-tris(carbazol-9-yl)-triphenylamine (TCTA) can efficiently passivate the anode interface of the Sb₂Se₃ solar cell. We fabricated the device by the vacuum thermal evaporation, and took ITO/TCTA (3.0 nm)/Sb₂Se₃ (50 nm)/C₆₀ (5.0 nm)/Alq₃ (3.0 nm)/Al as the device architecture, where Alq₃ is the tris(8-hydroxyquinolinato) aluminum. By introducing a TCTA layer, the open-circuit voltage is raised from 0.36 to 0.42 V, and the power conversion efficiency is significantly improved from 3.2% to 4.3%. The TCTA layer not only inhibits the chemical reaction between the ITO and Sb₂Se₃ during the annealing process but it also blocks the electron diffusion from Sb₂Se₃ to ITO anode. The enhanced performance is mainly attributed to the suppression of the charge recombination at the anode interface.

A physics-based analytical expression has been developed that predicts the charge, electrical field and potential distributions along the gated region of the GaN HEMT channel. Unlike the gradual channel approximation (GCA), the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied voltage. In addition, the model can capture the influence of mobility and channel temperature on the charge distribution trend. The comparison with the hydrodynamic (HD) numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration. The analytical nature of the model allows us to reduce the computational and time cost of the simulation. Also, it can be used as a core expression to develop a complete physics-based transistor IV model without GCA limitation.

In this work, the GaN p-MISFET with LPCVD-SiN_x is studied as a gate dielectric to improve device performance. By changing the Si/N stoichiometry of SiN_x, it is found that the channel hole mobility can be effectively enhanced with Si-rich SiN_x gate dielectric, which leads to a respectably improved drive current of GaN p-FET. The record high channel mobility of 19.4 cm²/(V∙s) was achieved in the device featuring an Enhancement-mode channel. Benefiting from the significantly improved channel mobility, the fabricated E-mode GaN p-MISFET is capable of delivering a decent-high current of 1.6 mA/mm, while simultaneously featuring a negative threshold-voltage (V_TH) of –2.3 V (defining at a stringent criteria of 10 μA/mm). The device also exhibits a well pinch-off at 0 V with low leakage current of 1 nA/mm. This suggests that a decent E-mode operation of the fabricated p-FET is obtained. In addition, the V_TH shows excellent stability, while the threshold-voltage hysteresis ΔV_TH is as small as 0.1 V for a gate voltage swing up to –10 V, which is among the best results reported in the literature. The results indicate that optimizing the Si/N stoichiometry of LPCVD-SiN_x is a promising approach to improve the device performance of GaN p-MISFET.

The self-heating effect severely limits device performance and reliability. Although some studies have revealed the heat distribution of β-Ga₂O₃ MOSFETs under biases, those devices are all have small areas and have difficulty reflecting practical conditions. This work demonstrated a multi-finger β-Ga₂O₃ MOSFET with a maximum drain current of 0.5 A, electrical characteristics were measured, and the heat dissipation of the device was investigated through infrared images. The relationship between device temperature and time/bias is analyzed.

This work demonstrates high-performance NiO/β-Ga₂O₃ vertical heterojunction diodes (HJDs) with double-layer junction termination extension (DL-JTE) consisting of two p-typed NiO layers with varied lengths. The bottom 60-nm p-NiO layer fully covers the β-Ga₂O₃ wafer, while the geometry of the upper 60-nm p-NiO layer is 10 μm larger than the square anode electrode. Compared with a single-layer JTE, the electric field concentration is inhibited by double-layer JTE structure effectively, resulting in the breakdown voltage being improved from 2020 to 2830 V. Moreover, double p-typed NiO layers allow more holes into the Ga₂O₃ drift layer to reduce drift resistance. The specific on-resistance is reduced from 1.93 to 1.34 mΩ·cm². The device with DL-JTE shows a power figure-of-merit (PFOM) of 5.98 GW/cm², which is 2.8 times larger than that of the conventional single-layer JTE structure. These results indicate that the double-layer JTE structure provides a viable way of fabricating high-performance Ga₂O₃ HJDs.

In this work, W/β-Ga₂O₃ Schottky barrier diodes, prepared using a confined magnetic field-based sputtering method, were analyzed at different operation temperatures. Firstly, Schottky barrier height increased with increasing temperature from 100 to 300 K and reached 1.03 eV at room temperature. The ideality factor decreased with increasing temperature and it was higher than 2 at 100 K. This apparent high value was related to the tunneling effect. Secondly, the series and on-resistances decreased with increasing operation temperature. Finally, the interfacial dislocation was extracted from the tunneling current. A high dislocation density was found, which indicates the domination of tunneling through dislocation in the transport mechanism. These findings are evidently helpful in designing better performance devices.

We present a series of Sm³⁺/Tb³⁺ co-doped CaMoO₄ phosphors synthesized by an efficient method of microwave-assisted heating. The prepared CaMoO₄ samples were characterized by X-ray diffraction, photoluminescence, and Commission Internationale de l’Elcairage (CIE) chromaticity diagram. The X-ray diffraction results confirmed that all of the synthesized CaMoO₄ samples are crystallized in a pure tetragonal phase. The photoluminescence spectra significantly show both red- and green emission in the synthesized Sm³⁺/Tb³⁺ co-doped CaMoO₄ phosphors. It is obvious that the variations in the intensity ratio of red/green emission depend on the molar ratio of Sm³⁺/Tb³⁺ co-doping and dominate the CIE color coordinates on the chromaticity diagram. The investigations evidence that the light-emitting region of Sm³⁺/Tb³⁺ co-doped CaMoO₄ phosphors can be controlled by adjusting the molar ratio of Sm³⁺/Tb³⁺ ions, acting as advanced color-tunable phosphors for white-LEDs.