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Ga2O3 has been considered as one of the most suitable materials for x-ray detection, but its x-ray detection performance is still at a low level due to the limitation of its quality and absorbance, especially for hard x-ray. In this work, the effects of growth temperature and miscut angle of the sapphire substrate on the crystal quality of Ga2O3 thin films were investigated based on the MOCVD technique. It was found that the crystal growth mode was transformed from island growth to step-flow growth using miscut sapphire substrates and increasing growth temperature, which was accompanied by the improvement of the crystal quality and the reduction of the density of trapped states. Ga2O3 films with optimal crystal quality were finally prepared on a 4° miscut substrate at 900 °C. The x-ray detector based on this film shows good hard x-ray response with a sensitivity of 3.72 × 105μC·Gyair−1·cm−2. Furthermore, the impacts of Ga2O3 film crystal quality and trap density on the x-ray detector were investigated in depth, and the mechanism of the photoconductive gain of the Ga2O3 thin-film x-ray detector was analyzed. [ABSTRACT FROM AUTHOR]

This work investigated the single-event effects (SEE) of NiO/β-Ga2O3 heterojunction diodes (HJDs) irradiated by 1.86 GeV tantalum ions with linear energy transfer over 80 MeV cm2/mg. The HJDs exhibited radiation responses with the early single-event leakage current (SELC) degradation until the fatal single-event burnout (SEB) failure, which was far below their breakdown voltages. Meanwhile, the surface morphology revealed the SELC damage expressed as burnout of topside NiO and metal stacks, while the SEB damage was observed as a burned hole in the β-Ga2O3 epitaxial layer. According to technology computer aided design simulations, the thicker p-type region in HJDs could further alleviate the electric field crowding effect exacerbated by the heavy-ion strike because of the extension of charge distribution in the p-type region. The SEB threshold was raised to 250 V by thickening the NiO layer to 300 nm. As for the SELC degradation process along with the burnout of topside stacks in HJDs, we supposed the probable reason was the intolerance of NiO to the high electric field under the SEE. This paper analyzed the SEE mechanism in β-Ga2O3 diodes and paved the way for heavy-ion irradiation hardening. [ABSTRACT FROM AUTHOR]

High-performance radiation detectors are essential in many sectors spanning medical diagnostics, nuclear control, and particle physics. Ultrawide bandgap semiconductor materials have become one of the most promising candidates due to their excellent performance. Here, based on β-Ga2O3, a Schottky diode-type alpha particle detector was demonstrated. In order to reduce the reverse leakage current of the large-area device, the metal-oxide electrode PtOx was introduced to form high-barrier contacts (1.83 eV) with Ga2O3. The device exhibits a low leakage current density of 63 pA/cm2 at −100 V and apparent energy spectra of 241Am generated alpha particles with an energy of 5.486 MeV at various reverse voltages from −40 to −120 V. The charge collection efficiency (CCE) and energy resolution of the device (at −120 V) are 31.7% and 15.3%, respectively. Meanwhile, the mechanism of interaction between alpha particles and β-Ga2O3 was analyzed, and a 45° oblique incidence was adopted to increase the deposited energy of alpha particles in the depletion region. Furthermore, the differences between actual CCE and theoretical CCE are investigated as guidance for further improving detector performance. This work reveals the great potential and good prospects of Ga2O3 as an economical, efficient, and radiation-resistant ionizing radiation detector. [ABSTRACT FROM AUTHOR]

Soft x-ray detectors play crucial roles in biology, chemistry, and lithography. Current soft x-ray detectors suffer from insufficient responsivity (R), excessively large cell area, and limited stability. Here, the β-Ga2O3 soft x-ray detector is constructed, and the effects of varying the sensitive layer thickness and voltage on the soft x-ray detection characteristics of the device are explored. Meanwhile, the mechanism of the multiplication ionization process from soft x-ray and the photoconductivity gain on the photoresponse performance of the device are analyzed. The device obtains the R up to 3.05 × 103 A/W under 300 eV soft x-ray irradiation at the synchrotron beamline, which is about 1.19 × 104 times higher than that of the conventional device. The Ga2O3 device also maintains stable operation under long-term irradiation and multicycle switching. These results indicate that Ga2O3 is an ideal candidate material for soft x-ray detection, which has great potential for applications such as imaging of biological cells. [ABSTRACT FROM AUTHOR]

Beta phase gallium oxide (β-Ga2O3) is emerging as a promising material for space applications due to its unique properties and potential high performance in extreme environments. In this work, we systematically study the impact of β-Ga2O3 Schottky barrier diodes (SBDs) under a high fluence neutron irradiation to explore the degradation mechanism of the devices. After irradiated by neutrons with an average energy of 1–2 MeV and a dose rate of 1.3 × 1012 cm−2 s−1, SBDs with a homoepitaxial layer suffered serious performance degradation. The main manifestation of this degradation was a substantial increase in on-resistance, which rose from 3.9 to 3.5 × 108 mΩ·cm2 under the aforementioned irradiation conditions. The appearance of amorphous/polycrystalline striped lattice damage in the epitaxial layer as well as the presence of deep-level defects caused by oxygen vacancies are factors related to this phenomenon. The simulation revealed that the capture reaction of neutrons and Ga elements is the primary cause of neutron irradiation. This reaction generates high-energy beta- particles (β-particles) resulting in the formation of defects. This paper reveals the degradation mechanism of β-Ga2O3 SBDs under neutron irradiation and provides a possible design roadmap for radiation-resistant β-Ga2O3 power devices. Moreover, a high-temperature oxygen annealing process was implemented, which proved to be in restoring the device performance. [ABSTRACT FROM AUTHOR]

Vertical metal–oxide–semiconductor field effect transistor (MOSFET) is essential to the future application of ultrawide bandgap β-Ga2O3. In this work, we demonstrated an enhancement-mode β-Ga2O3 U-shaped gate trench vertical metal–oxide–semiconductor field effect transistor (UMOSFET) featuring a current blocking layer (CBL). The CBL was realized by high-temperature annealing under oxygen ambient, which provided electrical isolation between the source and drain electrodes. The CBL thicknesses of different annealing temperatures were derived from C–V measurements and the Fermi level position of the sample surfaces of different annealing temperature was characterized by x-ray photoelectron spectroscopy measurements, indicating good process controllability. Furthermore, photoluminescence spectra were measured to study the effect of oxygen annealing. The fabricated UMOSFET showed normally off with a Vth of 11.5 V, an on-state resistance of 1.48 Ω cm2, a maximum on-state current of 11 A/cm2, an on–off ratio of 6 × 104, and a three-terminal breakdown voltage over 100 V. This work paves a way to form a CBL and broadens the design space for high-power β-Ga2O3 vertical transistors. [ABSTRACT FROM AUTHOR]

High tunability of photoresponse characteristics under work conditions is desired for a single solar-blind photodetector to be applied in multifarious fields. Three-terminal metal–oxide–semiconductor field-effect phototransistors have shown excellent controllability of performance, but the hysteresis issue impedes their stable operation. In this work, the metal–semiconductor field-effect phototransistor based on the exfoliated Ga2O3 microflake and graphene thin film is demonstrated. The high-quality quasi-van der Waals interface between Ga2O3 and graphene eliminates the hysteresis issue and generates a subthreshold swing as low as 69.4 mV/dec. By regulating gate voltage (Vg), the dominated mechanism of photocurrent generation in the device can be tuned continuously from the fast photoconduction effect to photogating effect with high photogain. Accordingly, the responsivity, dark current, detectivity, rejection ratio, and decay time of the device can be well adjusted by the Vg. At Vg = −1 V and a source to drain voltage of 2 V, the device shows excellent performance with a responsivity of 2.82 × 103 A/W, a rejection ratio of 5.88 × 105, and a detectivity of 2.67 × 1015 Jones under 254 nm illumination. This work shows the possibility of realizing highly tunable solar-blind photodetectors to meet the requirements for different application fields by introducing gate voltage modulation. [ABSTRACT FROM AUTHOR]

In this Letter, we report a high-performance NiO/β-Ga2O3 pn heterojunction diode with an optimized interface by annealing. The electrical characteristics of the pn diode without annealing (PND) and with annealing (APND) are studied systematically. The APND device has a lower specific on-resistance of 4.1 mΩ cm2, compared to that of the PND, 5.4 mΩ cm2. Moreover, for the APND, a high breakdown voltage of 1630 V with lower leakage current is achieved, which is 730 V higher than that of the PND. The enhanced electrical performance of the APND leads to a record high power figure of merit of 0.65 GW/cm2 in Ga2O3-based pn diodes, which is among the best reported results in Ga2O3 power devices. In addition, the interface trap density of the diode decreases from 1.04 × 1012 to 1.33 × 1011 eV−1 cm−2 after annealing, contributing to much lower hysteresis. Simultaneously, the ideality factor n for the APND is steady at elevated temperatures due to the stable interface. The results of C − V characteristics reveal the bulk defects inside the nickel oxide film grown by sputtering, which are calculated by high- and low-frequency capacitance methods. X-ray photoelectron spectroscopy of NiO illustrates the reasons for the changes in the concentration of holes and defects in the film before and after annealing. This work paves the way for further improving the performance of Ga2O3 diode via interface engineering. [ABSTRACT FROM AUTHOR]