Effective Leakage Current Reduction in GaN Ultraviolet Avalanche Photodiodes With an Ion-Implantation Isolation Method

We report high-performance homojunction GaN avalanche photodiodes (APDs) grown on a low-defect GaN substrate and fabricated with an ion-implantation isolation method. High-quality p-i-n GaN layers were grown using metalorganic chemical vapor deposition (MOCVD), and an effective device isolation method using optimized nitrogen ion implantation was developed to provide significant leakage current suppression on the etched mesa sidewalls. Fabricated GaN APDs showed an ultralow dark current density <; 10
^-9
A/cm
²
up to 50% of the avalanching breakdown voltage region and achieved a photocurrent gain of >106 at a reverse bias of 71.5 V under deep-ultraviolet (DUV) illumination at λ = 280 nm. A further temperature-dependent study of the dark current indicated that a trap-assisted tunneling process predominates the leakage current component that also contributes to the carrier multiplication process near the avalanching breakdown.