Low Resistance Ohmic Contact of Zn to the Polycrystalline Nitrogen-Doped P-Type $\upbeta$-Ga2O3 Film with Post-Annealing Studies

The effective p-type doping in $\beta-\text{Ga}_{2} \mathrm{O}_{3}$ is a major challenge for its high power applications. In this study, the nitrogen-doped polycrystalline $\beta-\text{Ga}_{2} \mathrm{O}_{3}$ film with improved p-type conductivity was fabricated via the thermal oxidation of the un-doped GaN in the $\mathrm{N}_{2} \mathrm{O}$ atmosphere at 1000° C, and zinc electrodes were fabricated by sputtering, followed by rapid thermal annealing (RTA). In order to form a high-quality ohmic contact, the electrical properties of the $\beta-\text{Ga}_{2} \mathrm{O}_{3}$ films were investigated at the various electrode annealing temperatures. At the electrode annealing temperature of 415° C, the $\beta-\text{Ga}_{2} \mathrm{O}_{3}$ film exhibited the optimal electrical properties. In the vacuum test environment, its room temperature Hall hole concentration is $2.106 \times 10^{18} \text{cm}^{-3}$, the Hall resistivity is $0.098 \Omega \cdot \text{cm}$, the Hall hole mobility is $19.656 \text{cm}^{2} \cdot \mathrm{V}^{-1} \mathrm{s}^{-1}$, and the acceptor ionization energy is 0.078 eV. It's a remarkable improvement in the p-type conductivity. Also at the annealing temperature of 415° C, Zn interfacial diffusion from the contact into $\beta-\text{Ga}_{2} \mathrm{O}_{3}$ is observed. This study shows nitrogen doping improves $\beta-\text{Ga}_{2} \mathrm{O}_{3}$'s p-type properties and Zn can form good ohmic contact with it through interface engineering, laying the groundwork for using $\beta-\text{Ga}_{2} \mathrm{O}_{3}$ in enhancement mode high-power MOSFETs.