The strong bonding in wide bandgap semiconductors gives them an intrinsic radiation hardness. Their suitability for space missions or military applications, where issues of radiation tolerance are critical, is widely known. Especially β-Ga₂O₃, an ultra-wide bandgap material, is attracting interest for power electronics and solar-blind ultraviolet detection. Beside its superior thermal and chemical stabilities, the effects of radiation damage on Ga₂O₃ are of fundamental interest in space-based and some terrestrial applications. We review the effect on the material properties and device characteristics of proton, electron, X-ray, gamma ray and neutron irradiation of β-Ga₂O₃ electronic and optoelectronic devices under conditions relevant to low earth orbit of satellites containing these types of devices.

Carrier removal rates and electron and hole trap densities in β-Ga₂O₃ films grown by hydride vapor phase epitaxy (HVPE) and irradiated with 18 MeV α-particles and 20 MeV protons were measured and compared to the results of modeling. The electron removal rates for proton and α-radiation were found to be close to the theoretical production rates of vacancies, whereas the concentrations of major electron and hole traps were much lower, suggesting that the main process responsible for carrier removal is the formation of neutral complexes between vacancies and shallow donors. There is a concurrent decrease in the diffusion length of nonequilibrium charge carriers after irradiation, which correlates with the increase in density of the main electron traps E2* at E_c − (0.75–0.78) eV, E3 at E_c − (0.95–1.05) eV, and E4 at E_c − 1.2 eV. The introduction rates of these traps are similar for the 18 MeV α-particles and 20 MeV protons and are much lower than the carrier removal rates.

The development of thermally stable contacts capable of high temperature operation are necessary for Ga₂O₃ high power rectifiers. We have measured the electrical characteristics of sputter-deposited W Schottky contacts with Au overlayers for reducing sheet resistance on n-type Ga₂O₃ before and after device operation up to 500°C. Assuming thermionic emission is dominant, the extracted barrier height decreases with measurement temperature from 0.97 eV (25°C) to 0.39 eV (500°C) while showing little change from its initial value of 0.97 eV after cooling down from each respective operation temperature. The room temperature value is comparable to that obtained by determining the energy difference between binding energy of the Ga 3d core level and the valence band of the Ga₂O₃ when W is present, 0.80 ± 0.2 eV in this case. The Richardson constant was 54.05 A.cm⁻².K⁻² for W and the effective Schottky barrier height at zero bias (eΦ_b0) was 0.92 eV from temperature-dependent current-voltage characteristics. The temperature coefficient for reverse breakdown voltage was 0.16 V/K for W/Au and 0.12 V/K for Ni/Au. The W-based contacts are more thermally stable than conventional Ni-based Schottkies on Ga₂O₃ but do show evidence of Ga migration through the contact after 500°C device operation.

There is interest in developing large area Ga₂O₃ rectifiers for applications in hybrid power converters. Vertical geometry, Schottky rectifiers with area 1.2 × 1.2 mm² fabricated on thick (8μm), undoped (n = 4.4 × 10¹⁵ cm⁻³) β-Ga₂O₃ epitaxial layers oN conducting bulk substrates exhibit both high forward current (1A in pulsed mode) and reverse breakdown voltage (V_B = 760V). This breakdown voltage was ∼200V higher than rectifiers without the presence of a bilayer SiO₂/ SiN_x field plate. This edge termination is critical for obtaining high breakdown voltage by reducing electric field crowding around the metal contact periphery. Optimization of the field plate design is still needed, since devices are observed experimentally to breakdown at the contact periphery. When purposely driven to failure at high reverse bias, pits are observed in the high field regions at the edge of the contact. The specific on-resistance (R_on) for these large area rectifiers was 22 mΩ.cm⁻², with a figure-of-merit V_B²/Ron of 26 MW.cm⁻². The potential of Ga₂O₃ for power electronics is clear when it is realized that these values are still an order of magnitude lower than theoretical values. The diode on-off ratio was in the range 2.7 × 10⁷–2.2 × 10⁹ when switching from +1.5V forward bias to 1–100V reverse bias.

The performance of arrays consisting of 21 β-Ga₂O₃ field-plated rectifiers fabricated on thick epitaxial layers (n-type carrier concentration ∼1.6 × 10¹⁶ cm⁻³) grown on conducting substrates (carrier concentration 3 × 10¹⁹ cm⁻³) is reported. We show that by interconnecting the output of 21 smaller (0.4 × 0.4 mm² to 1 × 1 mm², total area 0.09 cm²) individual rectifiers using e-beam deposited Au, we can achieve a high total forward output current of 33.2 A, at 4.25 V in the single-sweep voltage mode, and a low forward turn-on voltage of 2.9 V (defined at 100 A cm⁻²) and maintain a reverse breakdown voltage of 240 V (defined at 1 μA cm⁻²). The current density was 376 A cm⁻², and the on-state resistance was 0.012 Ω cm². The total forward current was 10 A at 1.9 V and 22 A at 3 V. The power figure-of-merit for the array, V_B²/R_ON, was 4.8 MW cm⁻², with a reverse recovery time of individual rectifiers of 32 ns. The on/off ratio of the rectifier array was in the range of 10⁵–10¹⁰ for +1 V/−1 to −100 V.

The commonly used n-type dopants, Si and Sn, were implanted into bulk (−201) β-Ga₂O₃ over a 2 order of magnitude dose range and annealed at temperatures from 1000–1150°C. The original lattice parameters were restored by annealing at 1150°C for the highest dose Si implants, while only partial recovery was observed in Sn implanted samples. The Sn implanted samples had overall lower lattice parameters compared to the Si implanted samples, indicating that Sn generates tensile strain in the Ga₂O₃ lattice. The rocking curve FWHM was observed to increase with the annealing process, indicating that the annealing process does not improve the crystal quality. Transmission electron microscopy showed removal of the end-of-range lattice damage after 1150°C anneals of the heaviest implanted species, Sn. Cathodoluminescence at 5K showed recovery of intensity of the common UV band around 3.2 eV after annealing. Secondary Ion Mass Spectrometry profiling showed the presence of concentration-dependent diffusion of both Si and Sn, with values for diffusivity at 1150°C of 9.5 × 10⁻¹³ cm.s⁻¹ for Si and 1.7 × 10⁻¹³ cm.s⁻¹ for Sn obtained by fitting through the FLOOPS simulation package.