This article reviews the effects of radiation damage on GaN materials and devices such as light-emitting diodes and high electron mobility transistors. Protons, electrons and gamma rays typically produce point defects in GaN, in contrast to neutron damage which is dominated by more extended disordered regions. Regardless of the type of radiation, the electrical conductivity of the GaN is reduced through the introduction of trap states with thermal ionization energies deep in the forbidden bandgap. An important practical parameter is the carrier removal rate for each type of radiation since this determines the dose at which device degradation will occur. Many studies have shown that GaN is several orders of magnitude more resistant to radiation damage than GaAs, i.e. it can withstand radiation doses of at least two orders of magnitude higher than those degrading GaAs with a similar doping level. Many issues still have to be addressed. Among them are the strong asymmetry in carrier removal rates in n- and p-type GaN and interaction of radiation defects with Mg acceptors and the poor understanding of interaction of radiation defects in doped nitrides with the dislocations always present.

The wide bandgap semiconductors SiC and GaN are already commercialized as power devices that are used in the automotive, wireless, and industrial power markets, but their adoption into space and avionic applications is hindered by their susceptibility to permanent degradation and catastrophic failure from heavy-ion exposure. Efforts to space-qualify these wide bandgap power devices have revealed that they are susceptible to damage from the high-energy, heavy-ion space radiation environment (galactic cosmic rays) that cannot be shielded. In space-simulated conditions, GaN and SiC transistors have shown failure susceptibility at ∼50% of their nominal rated voltage. Similarly, SiC transistors are susceptible to radiation damage-induced degradation or failure under heavy-ion single-event effects testing conditions, reducing their utility in the space galactic cosmic ray environment. In SiC-based Schottky diodes, catastrophic single-event burnout (SEB) and other single-event effects (SEE) have been observed at ∼40% of the rated operating voltage, as well as an unacceptable degradation in leakage current at ∼20% of the rated operating voltage. The ultra-wide bandgap semiconductors Ga ₂ O ₃ , diamond and BN are also being explored for their higher power and higher operating temperature capabilities in power electronics and for solar-blind UV detectors. Ga ₂ O ₃ appears to be more resistant to displacement damage than GaN and SiC, as expected from a consideration of their average bond strengths. Diamond, a highly radiation-resistant material, is considered a nearly ideal material for radiation detection, particularly in high-energy physics applications. The response of diamond to radiation exposure depends strongly on the nature of the growth (natural vs chemical vapor deposition), but overall, diamond is radiation hard up to several MGy of photons and electrons, up to 10 ¹⁵ (neutrons and high energetic protons) cm ⁻² and >10 ¹⁵ pions cm ⁻² . BN is also radiation-hard to high proton and neutron doses, but h-BN undergoes a transition from sp ² to sp ³ hybridization as a consequence of the neutron induced damage with formation of c-BN. Much more basic research is needed on the response of both the wide and ultra-wide bandgap semiconductors to radiation, especially single event effects.

A review is given of reported trap states in the bandgaps of different polymorphs of the emerging ultrawide bandgap semiconductor Ga2O3. The commonly observed defect levels span the entire bandgap range in the three stable (β) or meta-stable polymorphs (α and ɛ) and are assigned either to impurities such as Fe or to native defects and their complexes. In the latter case, the defects can occur during crystal growth or by exposure to radiation. Such crystalline defects can adversely affect material properties critical to device operation of transistors and photodetectors, including gain, optical output, threshold voltage by reducing carrier mobility, and effective carrier concentration. The trapping effects lead to degraded device operating speed and are characterized by long recovery transients. There is still significant work to be done to correlate experimental results based on deep level transient spectroscopy and related optical spectroscopy techniques to density functional theory and the dominant impurities present in the various synthesis methods to understand the microscopic nature of defects in Ga2O3.

The potential of ultrawide-bandgap (UWBG) semiconductors has not been fully explored because of the difficulty of forming a p-n homojunction. In this study, a mixed-dimensional UWBG p-n heterojunction composed of a p-type diamond substrate and an n-type exfoliated β-Ga₂O₃ nanolayer has been demonstrated via a van der Waals interaction; this type of structure does not suffer from lattice mismatch. Rectifying current-voltage characteristics with a rectification ratio exceeding 10⁷ were obtained with a high reverse hard breakdown voltage of 135 V. This UWBG p-n heterojunction diode exhibited good thermal stability at elevated temperatures, retaining its high rectification ratio and low reverse leakage current. Excellent photoresponse characteristics, including responsivity (12 A W⁻¹), rejection ratio (8.5 × 10³), photo-to-dark-current ratio (3900), and fast response/decay characteristics, were observed from the diamond/β-Ga₂O₃ p-n heterojunction photodiode, showing no persistent photoconductivity. The mixed-dimensional p-n heterojunction diode based on two UWBG semiconductors (p-type diamond and n-type β-Ga₂O₃) can be used as a robust building block in next-generation power electronics and solar-blind optoelectronics.

Gallium oxide (Ga2O3) has been the subject of extensive research over the past decade due to its potential in next-generation power electronics and solar-blind ultraviolet (UV) photodetectors. While Ga2O3 exhibits promising material characteristics for applications in harsh environments, its commercial viability remains under debate, particularly when compared to materials such as aluminum nitride (AlN) and diamond, which possess superior intrinsic properties. This perspective addresses the critical challenges that currently impede the widespread commercialization of Ga2O3-based devices. These challenges include a relatively immature technology base, the difficulty in achieving stable p-type conductivity, inherently low thermal conductivity, the presence of crystallographic defects (nano- and micro-voids), and elevated fabrication costs, all of which negatively impact device reliability and scalability. Mitigation strategies, such as heterojunction implementation, the development of thermal management solutions such as wafer bonding, and defect passivation approaches, are also under investigation. The near-term feasibility of commercially viable Ga2O3-based power electronic devices is a central focus of this discussion. The current status is that Ga2O3 development is far advanced relative to either diamond or especially AlN power electronics but is hampered by lack of a broad base of substrate vendors and a compelling vision for device implementations that provide sufficient improvement over SiC power devices. There are strong geographic differences in device focus, with China prioritizing implementation in grid applications while the United States/Europe appear to consider Ga2O3 devices more for defense and aerospace applications.

The temperature dependence of conductivity, thermally stimulated current (TSC), photoinduced current transient spectroscopy (PICTS) and microcathodoluminescence (MCL) were studied for Czochralski-grown β-Ga₂O₃ doped with Mg. The crystals had resistivity of 4.5 × 10¹¹ Ω.cm at 450K. The activation energy of the conductivity in the dark was 1.3 eV. TSC spectra revealed deep traps with activation energy ∼ 1 eV. In PICTS, a minor peak with activation energy ∼0.8 eV, two major peaks with activation energy 1.05 eV and 1.35 eV, and a broad band corresponding to negative photoconductivity were observed. From the dependence of the peak amplitude on bias polarity, the 1.05 eV peak was attributed to a Mg-related hole trap at E_v+1.05 eV. The higher energy peak was assigned to electron emission from a deep electron trap at E_c-1.35 eV that pins the Fermi level. Photocurrent spectra showed deep traps with optical ionization thresholds at 2 eV and 2.3 eV. MCL spectra showed the presence of traps with peak emission energies at 3.1 eV, 2.81 eV, and 2.56 eV.