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 <tex-math notation="LaTeX">~</tex-math> 1.8 <tex-math notation="LaTeX">∘</tex-math> 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 <tex-math notation="LaTeX">$<$</tex-math> 10 <tex-math notation="LaTeX">⁻⁹</tex-math> A/cm <tex-math notation="LaTeX">²</tex-math> in the low-mid reverse bias voltage region prior to avalanche breakdown and achieved a current-limited photocurrent gain of <tex-math notation="LaTeX">$>$</tex-math> 10 <tex-math notation="LaTeX">⁷</tex-math> under deep-ultraviolet (DUV) illumination at <tex-math notation="LaTeX">λ</tex-math> <tex-math notation="LaTeX">$=$</tex-math> 280 nm and a reverse bias <tex-math notation="LaTeX">$-$</tex-math> 107 V. The total current density without illumination was in the order of 10 <tex-math notation="LaTeX">⁻⁵</tex-math> A/cm <tex-math notation="LaTeX">²</tex-math> 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.