P-type Li_yNi_1-x-yMg_xO: A promising ultrawide bandgap semiconductor for Ga₂O₃ power devices applications

Ultrawide bandgap (UWBG) semiconductors are essential for the next generation of power electronics, offering superior breakdown voltages, thermal stability, and energy efficiency compared to conventional materials. However, the absence of efficient p-type UWBG semiconductors has been a major challenge, limiting the development of complementary devices. In this study, we explored Li_yNi_1-x-yMg_xO as a potential p-type UWBG semiconductor, employing co-sputtering techniques to precisely control the Mg content by adjusting the power density applied to Mg target. X-ray diffraction (XRD) revealed enhanced (200) and (111) diffraction peaks with increasing Mg content, confirming successful incorporation of Mg into the NiO lattice. X-ray photoelectron spectroscopy (XPS) further validated the substitution of Ni by Mg atoms. As the Mg target power density increased from 0 to 1 W·cm^-2, the optical bandgap widened from 4.27 eV to 5.44 eV, with corresponding improvements in optical transmittance. Hall effect measurements indicated a decrease in hole concentration with a significant enhancement in hole mobility as Mg content increased and reached 33.39 cm²V^-1s^-1 for 17.80 % Mg fraction. Despite the higher Mg fraction increasing the band alignment with n-type β-Ga₂O₃, a reduction in turn-on voltage with increasing Mg fraction compared with Li-doped NiO/β-Ga₂O₃ heterojunction diode (HJD) and an impressive BV of -1450 V were observed for films containing 17.80 % Mg. Silvaco TCAD simulations attributed these variations to trap-assisted tunneling, likely facilitated by Mg-induced energy levels within the Li-doped NiO matrix, which contributed to the reduction in turn-on voltage. The favorable electrical and optical properties of Li_yNi_1-x-yMg_xO films, along with the successful integration of Li_yNi_1-x-yMg_xO with β-Ga₂O₃ for heterojunction devices, demonstrate that Li_yNi_1-x-yMg_xO is a promising candidate for future p-type materials in UWBG power device applications, particularly in conjunction with n-type β-Ga₂O₃ and other UWBG semiconductors.