Radiation Effects on Vertical β-Ga₂O₃ High-Power Diodes

The ultra-wide bandgap (UWBG) semiconductor, β-Ga₂O₃, has received extensive interest for compact, high-power, and extreme environment electronics, driven by its high breakdown field (8 MV/cm), shallow dopants, availability of melt-grown native substrates, and predicted superior radiation hardness. This is specifically compelling for space electronics where lightweight and radiation-hard devices are essential requirements. Despite these exceptional material properties, β-Ga₂O₃ suffers from a major limitation of absence of p-type doping that has restricted its primary power rectifier switches to n-type Schottky barrier diodes (SBDs). Although vertical β-Ga₂O₃ SBDs have achieved remarkable advancement in device design and performance metrices in recent years, the devices still suffer from early breakdown at Schottky junction due to low surface breakdown field of <3.5 MV/cm, defined by the limited metal/β-Ga₂O₃ Schottky barrier height (SBH) of ~1.5 eV[1]. Moreover, in space environments, power devices may fail from single-event burnout (SEB) caused by single energetic particles. This has led to significant derating of existing SiC power devices in space with the operation voltage being less than 50% of the target voltage rating. Compared to the more mature SiC technology, available reports on the SEB response of β-Ga₂O₃ devices is even more scarce. Hence, to extract the full UWBG material benefits of β-Ga₂O₃ devices in space electronics, it is important to investigate their SEB performance under different heavy-ion irradiation conditions and adapt their device structures to address the challenges of both high-voltage and harsh radiation environments.

Towards this goal, we explored vertical β-Ga₂O₃ SBDs with oxidized metal (PtO_x) contacts that can allow high breakdown field at the Schottky junction owing to its high SBH (≥ 2 eV) [1]. To counter the effect of increased turn-on voltage due to the high SBH, we also performed further engineering of the Schottky contact with a thin (~1.5 nm) interlayer of Pt to form PtO_x/Pt/β-Ga₂O₃ SBDs. A systematic study of the vertical SBDs was performed with the three types of anode contacts, Pt/β-Ga₂O₃, PtO_x/Pt/β-Ga₂O₃, and PtO_x/β-Ga₂O₃, on halide vapor phase epitaxy (HVPE)-grown (001) β-Ga₂O₃ wafers of ~10 µm drift layer (doping ~1×10¹⁶ cm^-3). To reduce field crowding at the edges, we also integrated high-permittivity (κ) dielectric ZrO₂ (κ~26) field-plates in the SBDs. With the enhanced field management at both Schottky contact and edges, the PtO_x/β-Ga₂O₃ SBDs exhibited the highest breakdown voltage of 2.72 kV while the composite contact PtO_x/thin Pt/β-Ga₂O₃ SBDs enabled better efficiency with both reasonably high breakdown voltage (2.34 kV) and lower turn-on voltage by 0.6 V than PtO_x/β-Ga₂O₃ .

Subsequently, we studied SEB effects in the field-plate vertical β-Ga₂O₃ SBDs with Pt and PtO_x contacts by irradiating them with Cf-252 fission fragments and oxygen ions [2, 3]. The PtO_x/β-Ga₂O₃ SBDs allowed higher SEB voltage (450 V) than Pt//β-Ga₂O₃ (310 V) under Cf-252 irradiation. With the oxygen ion irradiation, a similar trend of increased SEB voltage was achieved for PtO_x/β-Ga₂O₃ SBDs (400 V) compared to that of Pt/β-Ga₂O₃ (60 V) [2, 3]. The TCAD modeling showed the presence of high ion-induced peak field under the Schottky contact of the irradiated Pt/β-Ga₂O₃ SBDs at the SEB voltage, which led to its early destructive failure. The consistent trend of better SEB resistance with PtO_x contacts than Pt ones attests to its high field stability under heavy-ion irradiation, in addition to conventional high-voltage application. Thus, the integration of robust anode contacts with enhanced field termination techniques represents a promising pathway to realize radiation-hard β-Ga₂O₃ devices for future space electronics.

Refs: [1] E. Farzana et al, Appl. Phys. Lett. 123, 192102 (2023)
[2] R. M. Cadena et al, IEEE Trans. Nucl. Sci. 70(4), 363 (2023)
[3] S. Islam et al, IEEE Trans. Nucl. Sci., 71(4), 515, (2024)