A p-Type Wide Bandgap Ni x In 1– x O 1+δ Oxide Alloy with Enhanced Hole Mobility for High Rectifying p–n Heterojunction Diodes

Developing high-performance p-type wide bandgap oxide is a critical challenge for advanced electronics. Here, we report the successful synthesis of Ni_xIn_1-xO_1+δ alloy films via room-temperature magnetron cosputtering. Our alloying strategy directly addresses the long-standing low mobility issue in NiO by utilizing band structure engineering, specifically by alleviating the strong localization of its valence band maximum (VBM) through In orbital interaction. Through composition tuning, we achieved tunable conductivity from semi-insulating to robust p-type, and even degenerate p-type at high Ni content. The optimal alloy (x∼ 0.92) exhibited a significantly improved hole mobility of ∼0.84 cm² V^-1 s^-1, substantially exceeding that of conventional p-type NiO (<0.1 cm² V^-1 s^-1), while maintaining a high hole concentration (∼3 × 10¹⁸ cm^-3) and a wide bandgap (∼3.6 eV). For Ni-rich compositions (x ≥ 0.95), we confirmed degenerate p-type conductivity through Hall-effect measurement and X-ray photoelectron spectroscopy valence band analysis, demonstrating the Fermi level located below the VBM. Structural and electronic analyses indicated that In alloying enhanced crystallinity and optimized the electronic structure by promoting VBM dispersion. Leveraging these superior properties, we fabricated p-Ni_0.92In_0.08O_1+δ/n-ZnO heterojunction diodes with a remarkable rectification ratio of ∼4.1 × 10⁵, approximately 22 times higher than control p-NiO_1+δ/n-ZnO devices. Our findings establish Ni_xIn_1-xO_1+δ as a highly promising p-type wide bandgap material, paving the way for advanced bipolar oxide-based devices and transparent electronics.