【Domestic Papers】Two-regime degradation associated with carrier compensation and structural instability in NiO/β-Ga₂O₃ heterojunction diodes under 1864 MeV Ta-ion irradiation

Background

      As a representative ultrawide-bandgap semiconductor, β-Ga₂O₃ has a bandgap of approximately 4.8 eV and a high critical electric field, making it a promising candidate for next-generation high-voltage power devices. NiO/β-Ga₂O₃ heterojunction diodes, formed by integrating p-type NiO with n-type β-Ga₂O₃, can achieve low reverse leakage current and high blocking capability, showing potential for high-reliability power electronic systems. However, in space radiation environments, energetic heavy ions can generate defects, defect clusters, and latent tracks inside the device, leading to carrier compensation, leakage increase, forward conduction degradation, and even device failure. Previous studies have mainly focused on β-Ga₂O₃ Schottky devices or heterojunction devices under a single irradiation fluence, while a systematic understanding of the full degradation process of NiO/β-Ga₂O₃ heterojunction diodes over a wide fluence range, from electrical degradation to structural-damage-associated failure, remains insufficient.

Abstract

      This study systematically investigates the fluence-dependent degradation behavior of NiO/β-Ga₂O₃ heterojunction diodes under 1864 MeV Ta-ion irradiation. The devices were irradiated over a fluence range from 1 × 10⁸ to 1 × 10¹¹ ions/cm², and their electrical and structural evolution was analyzed using I–V, C–V, STEM, and SEM characterizations. The results show that in the low-fluence regime, the devices retain rectifying behavior, while the forward current density decreases, the specific on-resistance increases, and the reverse leakage current rises. C–V analysis further reveals a reduction in the net carrier concentration of the β-Ga₂O₃ drift layer with increasing fluence, indicating that degradation is mainly dominated by carrier compensation. When the fluence increases to approximately 1 × 10¹⁰ ions/cm², the rectifying behavior collapses and normal turn-on behavior is lost. Structural characterization further reveals high-density nanoscale latent tracks in the β-Ga₂O₃ drift layer and an interfacial warping of about 2 μm near the NiO/β-Ga₂O₃ junction. These results demonstrate a two-regime degradation mechanism in NiO/β-Ga₂O₃ heterojunction diodes under heavy-ion irradiation, evolving from low-fluence carrier compensation to high-fluence structural-damage-associated failure.

Highlights

      The fluence-dependent degradation behavior of NiO/β-Ga₂O₃heterojunction diodes under 1864 MeV Ta-ion irradiation was systematically revealed.

      A two-regime degradation mechanism was proposed, evolving from low-fluence carrier compensation to high-fluence failure associated with structural damage.

      C–Vmeasurements were used to quantitatively extract the variation in net carrier concentration in the β-Ga₂O₃drift layer, confirming that low-fluence degradation is mainly dominated by carrier compensation.

      By combining STEM and SEM characterizations, nanoscale latent tracks in the β-Ga₂O₃drift layer and interfacial warping near the NiO/β-Ga₂O₃junction were observed at high fluence.

      The correlation among electrical degradation, carrier compensation, latent-track accumulation, and structural damage under heavy-ion irradiation was established, providing a reference for radiation-reliability evaluation of β-Ga₂O₃ heterojunction power devices.

      This work demonstrates that NiO/β-Ga₂O₃ heterojunction diodes exhibit a clear two-regime degradation behavior under 1864 MeV Ta-ion irradiation. In the low-fluence regime, the devices retain rectifying behavior, and the degradation is mainly governed by carrier compensation in the β-Ga₂O₃ drift layer, as reflected by the reduction in net carrier concentration, degraded forward conduction, and increased on-resistance. When the fluence increases to approximately 1 × 10¹⁰ ions/cm², the rectification collapses, accompanied by high-density nanoscale latent tracks in the β-Ga₂O₃ drift layer and an interfacial warping of about 2 μm near the NiO/β-Ga₂O₃ junction. This study reveals the degradation mechanism of NiO/β-Ga₂O₃ heterojunction diodes from carrier compensation to structural-damage-associated failure under heavy-ion irradiation, providing an important reference for reliability evaluation and radiation-hardened design of β-Ga₂O₃ power devices in space radiation environments.

      This work was supported by the Natural Science Foundation of Guangdong Province (No. 2023A1515011079), the National Key Laboratory Foundation (No. JWS262800320), and the National Natural Science Foundation of China (No. 12305299).

Fig. 1. Structure of the NiO/β-Ga₂O₃ HJD. (a) Schematic cross-section. (b) Cross-sectional HAADF–STEM image with EDS elemental maps. (c) Optical micrograph of a fabricated device with a 1 × 1 mm² active area.

Fig. 2. SRIM-simulated ion trajectories and damage in β-Ga₂O₃. (a) Ion trajectories in the depth–lateral (Y) plane, showing a projected range of Rp≈55.2 μm. (b) Depth profile of the total vacancy concentration calculated for a fluence of 1×10¹¹ cm⁻².

Fig. 3. (a) Forward I-V characteristics of NiO/β-Ga₂O₃ HJDs measured before and after Ta SHI irradiation at different fluences; symbols indicate the extracted R_on,sp (right-hand axis). (b) Corresponding reverse I-V characteristics measured up to 200 V.

Fig. 4. (a) C–V and 1/C²–V characteristics of NiO/β-Ga₂O₃ HJDs before and after Ta SHI irradiation at different fluences. Filled symbols represent C–V (left axis), whereas open symbols represent 1/C²–V (right axis). (b) Net carrier concentration (N_net) profiles extracted from C–V measurements for the fresh device and irradiated devices up to 1×10⁹ ions/cm².

Fig. 5. Cross-sectional STEM images of the β-Ga₂O₃ drift layer after Ta SHI irradiation at 1×10¹⁰ ions/cm², showing SHI-induced latent tracks: (a) Low-magnification view. (b) High-magnification view.

Fig. 6. Cross-sectional SEM image of a representative NiO/β-Ga₂O₃ HJD irradiated at 1×10¹⁰ ions/cm², showing interfacial warping near the NiO/β-Ga₂O₃ junction (~2 µm).

DOI:

doi.org/10.1063/5.0332137