HVPE growth of bulk GaN with high conductivity for vertical devices

Abstract

Abstract The electrical properties of gallium nitride (GaN) substrate are crucial to the performance of vertical power devices. Bulk GaN substrates with carrier concentrations in the range from 6.7 × 1017 to 1.7 × 1019 cm−3 are grown by hydride vapor phase epitaxy. All samples show no obvious tensile stress regardless of the carrier concentration. Moreover, the mobility of Si-doped high-quality bulk GaN is superior to the GaN template with higher dislocation density at the same carrier concentration. The influence of carrier concentration on the performance of ohmic contact on N-face of Si-doped GaN is also carefully studied by circular transfer length measurement and rapid thermal annealing methods. The specific contact resistivity decreases monotonically with increase of carrier concentration, while it increases with the annealing temperature. The N-face contact becomes non-ohmic when the annealing temperature exceeds the limit value, which increases with the carrier concentration. The sample with carrier concentration of 1.7 × 1019 cm−3 still showed ohmic behavior after annealing at 450 °C. These results are not only useful to improve the electrical properties of N-type bulk GaN substrate, but also provide a potential solution for improving the efficiency of vertical devices in the future.