Low Leakage and High Gain GaN p-i-n Avalanche Photodiode With Shallow Bevel Mesa Edge Termination and Recessed Window

This work reports high-performance homojunction gallium nitride (GaN) p-i-n (PIN) avalanche photodiodes (APDs) grown on a low-defect GaN substrate and fabricated with an ~1.8° shallow-bevel-mesa edge termination. High-quality p-i-n GaN epitaxial layers were grown using metalorganic chemical vapor deposition (MOCVD), and the device edge termination was achieved by multistep pseudo gray-scale lithography followed by photoresist reflow and dry etching of the bevel mesa. Fabricated GaN APDs showed an ultralow dark current density $\lt 10^{-{9}}$ A/cm2 in the low-mid reverse bias voltage region prior to avalanche breakdown and achieved a current-limited photocurrent gain of $\gt 10^{{7}}$ under deep-ultraviolet (DUV) illumination at $\lambda =280$ nm and a reverse bias −107 V. The total current density without illumination was in the order of $10^{-{5}}$ A/cm2 at the onset of avalanche breakdown. The avalanche breakdown characteristic was confirmed by temperature-dependent J–V studies, with a derived positive temperature coefficient of 0.02 V/K for the breakdown voltage (BV). The analysis of the temperature-dependent reverse-bias characteristics indicated that the reverse leakage current components before avalanche could be attributed to trap-assisted tunneling (TAT) and phonon-assisted tunneling (PAT) processes.