Search for: All records

This study demonstrates a substantial enhancement of breakdown voltage in β-Ga2O3 Schottky barrier diodes through an approach that combines fast neutron irradiation with controlled post-irradiation electro-thermal annealing. Devices irradiated with 1 MeV neutrons at a high fluence of 1 × 1015 n/cm2 initially exhibited substantial degradation, including a drastic reduction in on-current and an increase in on-resistance. Electro-thermal testing, conducted through simultaneous current–voltage measurements while heating the devices up to 250 °C, resulted in significant recovery. After four cycles of electro-thermal testing, the devices demonstrated significant improvements in performance, with a substantial recovery of on-current and a reduction in on-resistance compared to the post-radiation condition, approaching pre-radiation levels. Most recovery occurred during the first two cycles, with diminishing improvements thereafter, indicating that thermally responsive radiation-induced traps were largely mitigated early in the process. Capacitance–voltage measurements revealed a substantial reduction in net carrier concentration, decreasing from 3.2 × 1016 cm−3 pre-radiation to 5.5 × 1015 cm−3 after the first electro-thermal testing cycle, indicating an over 82% reduction. Following the third cycle, the carrier concentration partially recovered to 9.9 × 1015 cm−3, reflecting a carrier removal rate of ∼22 cm−1. The breakdown voltage (Vbr) exhibited a remarkable enhancement, increasing from approximately 300 V to 1.28 kV (a ∼325% improvement) after the first electro-thermal testing, which can be attributed to the reduction in net carrier concentration by compensating radiation-induced traps. Subsequent testing reduced Vbr slightly to 940 V due to partial recovery of carrier concentration, but it remained significantly higher than pre-radiation levels. These findings demonstrate the potential of combining neutron irradiation with electro-thermal annealing to significantly enhance the voltage-blocking capability of β-Ga2O3 power devices, making them strong candidates for high-power applications in radiation-intense environments. 

This work demonstrates quasi-vertical β-Ga2O3 Schottky barrier diodes (SBDs) fabricated on c-plane sapphire substrates using an all-low-pressure chemical vapor deposition (LPCVD)-based, plasma-free process flow that integrates both epitaxial growth of a high-quality β-Ga2O3 heteroepitaxial film with in situ Ga-assisted β-Ga2O3 etching. A 6.3 μm thick (2̄01) oriented β-Ga2O3 epitaxial layer structure was grown on c-plane sapphire with 6° miscut, comprising a moderately Si-doped (2.1 × 1017 cm−3) 3.15 μm thick drift layer and a heavily doped (1 × 1019 cm−3) contact layer on an unintentionally doped buffer layer. Mesa isolation was achieved via Ga-assisted plasma-free LPCVD etching, producing ∼60° inclined mesa sidewalls with an etch depth of 3.6 μm. The fabricated SBDs exhibited excellent forward current–voltage characteristics, including a turn-on voltage of 1.22 V, an ideality factor of 1.29, and a Schottky barrier height of 0.83 eV. The minimum differential specific on-resistance was measured to be 8.6 mΩ cm2, and the devices demonstrated high current density capability (252 A/cm2 at 5 V). Capacitance–voltage analysis revealed a net carrier concentration of 2.1 × 1017 cm−3, uniformly distributed across the β-Ga2O3 drift layer. Temperature-dependent J–V–T measurements, conducted from 25 to 250 °C, revealed thermionic emission-dominated transport with strong thermal stability. The Schottky barrier height increased from 0.80 to 1.16 eV, and the ideality factor rose modestly from 1.31 to 1.42 over this temperature range. Reverse leakage current remained low, increasing from ∼5 × 10−6 A/cm2 at 25 °C to ∼1 × 10−4 A/cm2 at 250 °C, with the Ion/Ioff ratio decreasing from ∼1 × 107 to 5 × 105. The devices achieved breakdown voltages ranging from 73 to 100 V, corresponding to parallel-plate electric field strengths of 1.66–1.94 MV/cm. These results highlight the potential of LPCVD-grown and etched β-Ga2O3 devices for high-performance, thermally resilient power electronics applications. 

This work demonstrates an in situ etching technique for β-Ga2O3 using solid-source metallic gallium (Ga) in a low-pressure chemical vapor deposition (LPCVD) system, enabling clean, anisotropic, plasma damage-free etching. Etching behavior was systematically studied on (2¯01) β-Ga2O3 films and patterned (010) β-Ga2O3 substrates as a function of temperature (1000–1100 °C), Ar carrier gas flow (80–400 sccm) and Ga source-to-substrate distance (1–5 cm). The process exhibits vapor transport- and surface-reaction-limited behavior, with etch rates reaching a maximum of ∼2.25 µm/h on (010) substrates at 1050 °C and 2 cm spacing. Etch rates decrease sharply with increasing source-to-substrate distance due to reduced Ga vapor availability, while elevated temperatures enhance surface reaction kinetics through increased Ga reactivity and suboxide formation, leading to enhanced etch rates. In-plane anisotropy studies using radial trench patterns reveal that the (100) orientation produces the most stable etch front, characterized by smooth, vertical sidewalls and minimal lateral etching, consistent with its lowest surface free energy. In contrast, orientations such as (101), which possess higher surface energy, exhibit pronounced lateral etching and micro-faceting. As the trench orientation progressively deviates from (100), lateral etching increases. Facet evolution is observed between (100) and (1¯02), where stepped sidewalls composed of alternating (100) and (1¯02) segments progressively transition into a single inclined facet, which stabilizes along (100) or (1¯02) depending on the trench orientation. The (100)-aligned fins exhibit minimal bottom curvature, while (201)-aligned structures display increased under-etching and trench rounding. Collectively, these findings establish LPCVD-based in situ etching as a scalable, damage-free, and orientation-selective technique for fabricating high-aspect-ratio β-Ga2O3 3D structures in next-generation power devices.