P-type LiyNi1-x-yMgxO: A promising ultrawide bandgap semiconductor for Ga2O3 power devices applications

• Ultrawide bandgap p-type Li y Ni 1-x-y Mg x O thin films were successfully demonstrated for power device integration. • The optical bandgap was tunable from 4.27 eV to 5.44 eV by adjusting the Mg fraction in Li y Ni 1-x-y Mg x O. • A high hole mobility of 33.39 cm²V⁻¹s⁻¹ was achieved at 17.80 % Mg concentration. • A Li y Ni 1-x-y Mg x O/β-Ga₂O₃ heterojunction with a clean and well-defined interface was successfully demonstrated. • A breakdown voltage of ∼1450 V was obtained for the heterojunction diode using 17.80 % Mg in Li y Ni 1-x-y Mg x O. • The turn-on voltage decreased with increasing Mg content, enhancing carrier injection at the interface. 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 y Ni 1-x-y Mg x O 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 cm 2 V -1 s -1 for 17.80 % Mg fraction. Despite the higher Mg fraction increasing the band alignment with n-type β-Ga 2 O 3 , a reduction in turn-on voltage with increasing Mg fraction compared with Li-doped NiO/β-Ga 2 O 3 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 y Ni 1-x-y Mg x O films, along with the successful integration of Li y Ni 1-x-y Mg x O with β-Ga 2 O 3 for heterojunction devices, demonstrate that Li y Ni 1-x-y Mg x O is a promising candidate for future p-type materials in UWBG power device applications, particularly in conjunction with n-type β-Ga 2 O 3 and other UWBG semiconductors.