P-Type Doping Control of Magnetron Sputtered NiO for High Voltage UWBG Device Structures

Abstract

A major challenge in the design and fabrication of power devices from ultra-wide bandgap (UWBG) materials is the lack of a native shallow acceptor dopant for most materials in that class. P-Type regions in UWBG devices may alternatively be formed by the deposition of p-Type wide bandgap materials such as nickel oxide (NiO) to form heterojunctions. This work examines the effectiveness of the modulation of the acceptor concentration (NA) of magnetron sputtered NiO via the control of O2 partial pressure during sputtering. NiO/n+-Ga2O3 PN junctions are fabricated via sputtering using O2/Ar percentage ratios ranging from 0% to 12.5%. The acceptor doping and acceptor level characteristics are studied via the dependence of PN junction capacitance upon voltage, temperature and frequency. It is found that the NA can be controlled between 9×1017 cm-3 at 0% O2/Ar to 2×1018 cm-3 at 12.5% O2/Ar partial pressure. Studies of the capacitance of the diodes shows that the associated first ionization level of the Ni3+ vacancy thought to be responsible for the p-Type doping of the NiO is 0.35 eV, with suggestion of a second ionization level at 0.54 eV seen in the 0% O2/Ar sample. To demonstrate the feasibility of utilizing magnetron sputtered NiO in power devices, a lateral RESURF terminated Ga2O3 Schottky diode is fabricated. Charge balance to maximize breakdown voltage is demonstrated in the Schottky diode as a function of NiO RESURF thickness, showing the viability of NiO in high voltage power devices for field spreading regions such as RESURF layers and JTE structures.