A robust ohmic contact process with ultralow contact resistivity on p-GaN/AlGaN/GaN is demonstrated. An in-situ removal of GaO _X interfacial layer after contact metal deposition is developed. Using the novel Mg/Pt/Au stack as the contact metal, a stable ohmic contact is obtained after 450°C/300 s annealing with ohmic contact resistivity of $12 \Omega \cdot {\mathrm {mm}}$ ( $1.8\times 10^{-5}\, \Omega \cdot {\mathrm {cm}}^{2}$ ). A new ohmic contact formation mechanism on p-GaN/AlGaN/GaN is also proposed.

This study optimizes the CuO_x/Ga₂O₃ heterojunction diodes (HJDs) by tailoring the structural parameters of CuO_x layers. The hole concentration in the sputtered CuO_x was precisely controlled by adjusting the Ar/O₂ gas ratio. Experimental investigations and TCAD simulations were employed to systematically evaluate the impact of the CuO_x layer dimension and hole concentration on the electrical performance of HJDs. The results indicate that increasing the diameter dimension of the CuO_x layer or tuning the hole concentration to optimal values significantly enhances the breakdown voltage (V_B) of single-layer HJDs by mitigating the electric field crowing effects. Additionally, a double-layer CuO_x structure (p⁺ CuO_x/p⁻ CuO_x) was designed and optimized to achieve an ideal balance between the V_B and specific on-resistance (R_on,sp). This double-layer HJD demonstrated a high V_B of 2780 V and a low R_on,sp of 6.46 mΩ·cm², further yielding a power figure of merit of 1.2 GW/cm². These findings present a promising strategy for advancing the performance of Ga₂O₃ devices in power electronics applications.

Mg-doped spin-on-glass (SOG) treatment is employed as a simple and effective Mg doping method, which can lower the barrier height of p-GaN/metal and form robust Ni/Au Ohmic contact on p-GaN/AlGaN/GaN structure. After SOG treatment annealed at 870°C, the specific contact resistivity and contact resistivity of Ni/Au metal stack decreased from 1.3 × 10⁻³ Ω·cm² to 1.2 × 10⁻⁴ Ω·cm² and from 78.2 Ω·mm to 22.5 Ω·mm, respectively. The SOG treatment maintained a good surface morphology and effectively increased Mg concentration near the p-GaN surface, which could in situ decompose the dense GaO_X layer. In addition, the SOG treatment facilitated Ga out-diffusion from p-GaN layer, and the inversion process induced by Ni/Au-based p-GaN Ohmic annealing is more complete, ultimately forming a p-GaN/Au/NiO Ohmic stack with a favorable atomic arrangement interface. These results demonstrate the significant potential of SOG technology in the selective doping of p-GaN.