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p-type Cr2MnO4 with bandgap 3.01 eV was sputter deposited onto (2¯01) and (001) n-type or semi-insulating β-Ga2O3.The heterojunction of p-type CrMnO4 on n-type Ga2O3 is found to be type II, staggered gap, i.e., the band offsets are such that both the conduction and valence band edges of Ga2O3 are lower in energy than those of the Cr2MnO4. This creates a staggered band alignment, which can facilitate the separation of photogenerated electron-hole pairs. The valence band edge of Cr2MnO4 is higher than that of Ga2O3 by 1.82–1.93 eV depending on substrate orientation and doping, which means that holes in Cr2MnO4 would have a lower energy barrier to overcome to move into Ga2O3. Conversely, the conduction band edge of Cr2MnO4 is higher than that of Ga2O3 by 0.13–0.30 eV depending on substrate doping and orientation, which would create a barrier for electrons in Ga2O3 to move into Cr2MnO4. This heterojunction looks highly promising for p-n junction formation for advanced Ga2O3-based power rectifiers. 

Gallium oxide (Ga2O3) exists in different polymorphic forms, including the trigonal (α), monoclinic (β), cubic (γ), and orthorhombic (κ) phases, each exhibiting distinct structural and electronic properties. Among these, β-Ga2O3 is the most thermodynamically stable and widely studied for high-power electronics applications due to its ability to be grown as high-quality bulk crystals. However, metastable phases such as α-, γ-, and κ-Ga2O3 offer unique properties, including wider bandgap or strong polarization and ferroelectric characteristics, making them attractive for specialized applications. This paper summarizes the radiation hardness of these polymorphs by analyzing the reported changes in minority carrier diffusion length (LD) and carrier removal rates under various irradiation conditions, including protons, neutrons, alpha particles, and gamma rays. β-Ga2O3 demonstrates high radiation tolerance with LD reductions correlated to the introduction of electron traps (E2*, E3, and E4) and gallium–oxygen vacancy complexes (VGa–VO). α-Ga2O3 exhibits slightly better radiation hardness similar to κ-Ga2O3, which also shows minimal LD changes postirradiation, likely due to suppressed defect migration. γ-Ga2O3 is the least thermodynamically stable, but surprisingly is not susceptible to radiation-induced damage, and is stabilized under Ga-deficient conditions. The study highlights the role of polymorph-specific defect dynamics, doping concentrations, and nonuniform electrical properties in determining radiation hardness. We also discuss the effect of radiation exposure on the use of NiO/Ga2O3 heterojunction rectifiers that provide superior electrical performance relative to Schottky rectifiers. The presence of NiO does change some aspects of the response to radiation. Alloying with Al2O3 further modulates the bandgap of Ga2O3 and defect behavior, offering potentially tunable radiation tolerance. These findings provide critical insights into the radiation response of Ga2O3 polymorphs, with implications for their use in aerospace and radiation-hardened power electronics. Future research should focus on direct comparisons of polymorphs under identical irradiation conditions, defect identification, and annealing strategies to enhance radiation tolerance. 

Abstract Lateral Schottky or heterojunction rectifiers were irradiated with 10 MeV protons and neutrons. For proton irradiation, the forward current of both types of rectifiers decreased by approximately an order of magnitude, with a corresponding increase in on-state resistance. The resultant on/off ratio improved after irradiation because of the larger decrease in reverse current compared to forward current. Both types of rectifiers displayed a shift in forward current and RON curves to lower voltages after irradiation. This could be due to defects created by neutron irradiation introducing deep energy levels within the bandgap of AlN. These deep levels can trap charge carriers, reducing their mobility and increasing the on-state resistance. Transmission electron microscopy showed disorder created at the AlN/NiO interface by neutron irradiation. TCAD simulation was used to study the effects of irradiation with both protons and neutrons. The results confirmed that the irradiation caused a significant reduction in electron concentration and a small increase in the recombination rate. Neutron irradiation can also introduce interface states at the metal or oxide-semiconductor junction of the rectifier. These interface states can modify the effective Schottky barrier height, affecting the forward voltage drop and on-state resistance. 

Abstract 17 MeV proton irradiation at fluences from 3–7 × 10¹³cm⁻²of vertical geometry NiO/β-Ga₂O₃heterojunction rectifiers produced carrier removal rates in the range 120–150 cm⁻¹in the drift region. The forward current density decreased by up to 2 orders of magnitude for the highest fluence, while the reverse leakage current increased by a factor of ∼20. Low-temperature annealing methods are of interest for mitigating radiation damage in such devices where thermal annealing is not feasible at the temperatures needed to remove defects. While thermal annealing has previously been shown to produce a limited recovery of the damage under these conditions, athermal annealing by minority carrier injection from NiO into the Ga₂O₃has not previously been attempted. Forward bias annealing produced an increase in forward current and a partial recovery of the proton-induced damage. Since the minority carrier diffusion length is 150–200 nm in proton irradiated Ga₂O₃, recombination-enhanced annealing of point defects cannot be the mechanism for this recovery, and we suggest that electron wind force annealing occurs. 

Minority carrier diffusion length in undoped p-type gallium oxide was measured at various temperatures as a function of electron beam charge injection by electron beam-induced current technique in situ using a scanning electron microscope. The results demonstrate that charge injection into p-type β-gallium oxide leads to a significant linear increase in minority carrier diffusion length followed by its saturation. The effect was ascribed to trapping of non-equilibrium electrons (generated by a primary electron beam) on metastable native defect levels in the material, which in turn blocks recombination through these levels. While previous studies of the same material were focused on probing a non-equilibrium carrier recombination by purely optical means (cathodoluminescence), in this work, the impact of charge injection on minority carrier diffusion was investigated. The activation energy of ∼0.072 eV, obtained for the phenomenon of interest, is consistent with the involvement of Ga vacancy-related defects. 

Thermal annealing is commonly used in fabrication processing and/or performance enhancement of electronic and opto-electronic devices. In this study, we investigate an alternative approach, where high current density pulses are used instead of high temperature. The basic premise is that the electron wind force, resulting from the momentum loss of high-energy electrons at defect sites, is capable of mobilizing internal defects. The proposed technique is demonstrated on commercially available optoelectronic devices with two different initial conditions. The first study involved a thermally degraded edge-emitting laser diode. About 90% of the resulting increase in forward current was mitigated by the proposed annealing technique where very low duty cycle was used to suppress any temperature rise. The second study was more challenging, where a pristine vertical-cavity surface-emitting laser (VCSEL) was subjected to similar processing to see if the technique can enhance performance. Encouragingly, this treatment yielded a notable improvement of over 20% in the forward current. These findings underscore the potential of electropulsing as an efficient in-operando technique for damage recovery and performance enhancement in optoelectronic devices. 

Abstract In this study, we explore the rejuvenation of a Zener diode degraded by high electrical stress, leading to a leftward shift, and broadening of the Zener breakdown voltage knee, alongside a 57% reduction in forward current. We employed a non-thermal annealing method involving high-density electric pulses with short pulse width and low frequency. The annealing process took <30 s at near-ambient temperature. Raman spectroscopy supports the electrical characterization, showing enhancement in crystallinity to explain the restoration of the breakdown knee followed by improvement in forward current by ∼85%. 

Strain plays an important role in the performance and reliability of AlGaN/GaN high electron mobility transistors (HEMTs). However, the impact of strain on the performance of proton irradiated GaN HEMTs is yet unknown. In this study, we investigated the effects of strain relaxation on the properties of proton irradiated AlGaN/GaN HEMTs. Controlled strain relief is achieved locally using the substrate micro-trench technique. The strain relieved devices experienced a relatively smaller increase of strain after 5 MeV proton irradiation at a fluence of 5 × 1014 cm−2 compared to the non-strain relieved devices, i.e., the pristine devices. After proton irradiation, both pristine and strain relieved devices demonstrate a reduction of drain saturation current (Ids,sat), maximum transconductance (Gm), carrier density (ns), and mobility (μn). Depending on the bias conditions the pristine devices exhibit up to 32% reduction of Ids,sat, 38% reduction of Gm, 15% reduction of ns, and 48% reduction of μn values. In contrast, the strain relieved devices show only up to 13% reduction of Ids,sat, 11% reduction of Gm, 9% reduction of ns, and 30% reduction of μn values. In addition, the locally strain relieved devices show smaller positive shift of threshold voltage compared to the pristine devices after proton irradiation. The less detrimental impact of proton irradiation on the transport properties of strain relieved devices could be attributed to reduced point defect density producing lower trap center densities, and evolution of lower operation related stresses due to lower initial residual strain. 

Abstract Radiation susceptibility of electronic devices is commonly studied as a function of radiation energetics and device physics. Often overlooked is the presence or magnitude of the electrical field, which we hypothesize to play an influential role in low energy radiation. Accordingly, we present a comprehensive study of low-energy proton irradiation on gallium nitride high electron mobility transistors (HEMTs), turning the transistor ON or OFF during irradiation. Commercially available GaN HEMTs were exposed to 300 keV proton irradiation at fluences varying from 3.76 × 10¹²to 3.76 × 10¹⁴cm², and the electrical performance was evaluated in terms of forward saturation current, transconductance, and threshold voltage. The results demonstrate that the presence of an electrical field makes it more susceptible to proton irradiation. The decrease of 12.4% in forward saturation and 19% in transconductance at the lowest fluence in ON mode suggests that both carrier density and mobility are reduced after irradiation. Additionally, a positive shift in threshold voltage (0.32 V and 0.09 V in ON and OFF mode, respectively) indicates the generation of acceptor-like traps due to proton bombardment. high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis reveal significant defects introduction and atom intermixing near AlGaN/GaN interfaces and within the GaN layer after the highest irradiation dose employed in this study. According toin-situRaman spectroscopy, defects caused by irradiation can lead to a rise in self-heating and a considerable increase in (∼750 times) thermoelastic stress in the GaN layer during device operation. The findings indicate device engineering or electrical biasing protocol must be employed to compensate for radiation-induced defects formed during proton irradiation to improve device durability and reliability. 

It has recently been demonstrated that electron beam injection into p-type β-gallium oxide leads to a significant linear increase in minority carrier diffusion length with injection duration, followed by its saturation. The effect was ascribed to trapping of non-equilibrium electrons (generated by a primary electron beam) at meta-stable native defect levels in the material, which in turn blocks recombination through these levels. In this work, in contrast to previous studies, the effect of electron injection in p-type Ga2O3 was investigated using cathodoluminescence technique in situ in scanning electron microscope, thus providing insight into minority carrier lifetime behavior under electron beam irradiation. The activation energy of ∼0.3 eV, obtained for the phenomenon of interest, is consistent with the involvement of Ga vacancy-related defects.