Realization of high-performance hetero-field-effect-transistor-type ultraviolet photosensors using p-type GaN comprising three-dimensional island crystals

Abstract

High-performance AlGaN/AlGaN hetero-field-effect-transistor (HFET)-type photosensors with high photosensitivity were fabricated using p-type GaN comprising three-dimensional island crystals. The p-type GaN layers were grown on AlGaN layers at a high AlN molar fraction, and the area of p-type GaN comprising three-dimensional island crystals increased as the thickness of the p-type GaN film decreased, resulting in a reduced p-type GaN coverage ratio. The p-type GaN layers comprising three-dimensional island crystals and showing low coverage ratios were then used to fabricate HFET-type photosensors with high photosensitivity. A high light sensitivity of 1.5 × 104 A/W was obtained at a source–drain voltage (VSD) of 0.5 V for a photosensor with a p-type GaN thickness of 20 nm. Moreover, the dark current was suppressed to 10−10 A/mm and the photosensor achieved an extremely high photocurrent to dark current density ratio.