Valence-band engineering of robust p -type Ni x Ga1− x O enabling Ga2O3 p–n bipolar junction

The absence of a reliable p-type ultrawide bandgap (UWBG) semiconductor remains a fundamental obstacle to the realization of bipolar Ga2O3-based power devices. Here, we demonstrate valence-band engineering in Ni-alloyed Ga2O3 (NixGa1−xO) to achieve robust p-type conduction. Strong Ni 3d-O 2p hybridization in NixGa1−xO effectively reshapes the valence band structures, elevating the valence band maximum and enabling hole transport for x > 0.3. Increasing Ni composition from 0.32 to 0.62 in NixGa1−xO reduces the hopping activation energy to 0.06 eV, yielding a hole concentration of ∼1018 cm−3 and resistivity near 40 Ω cm while maintaining a wide bandgap of 4.5–4.1 eV. The constructed p-Ni0.62Ga0.38O/n-Ga2O3 diode exhibits distinct forward bipolar conduction modulation with rectification ratios >1010 at ±3 V, and a bilayer Ni0.32Ga0.68O/Ni0.62Ga0.38O structure enhances reverse blocking to 2.4 kV. These findings establish Ni-alloyed Ga2O3 as a robust p-type UWBG material for bipolar Ga2O3 power electronics.