Surface smoothing with BCl3 plasma post-treatment to improve the performance of GaN avalanche photodiodes

Abstract

This paper reports a plasma post-treatment technique to improve the performance of GaN ultraviolet avalanche photodiodes (APDs). A BCl3-based plasma post-etching technique was developed to smooth the roughened GaN surface after inductively-coupled-plasma etching. Atomic-scale surface roughness around 0.278 nm rms and photoluminescence intensity more than doubled were achieved after the post-treatment. The surface smoothing technique was applied to the fabrication process of double-mesa structure GaN APDs grown on a sapphire substrate. Compared to the non-treated APDs, the post-treated GaN APDs show high field leakage current suppressed more than two orders and the average gain increased from 2 × 104 to 1 × 105, indicating the low surface damage after BCl3 plasma post-treatment. For the GaN APDs fabricated into a 3 × 3 array, the devices show uniform distribution of the breakdown voltages after the plasma post-treatment.