Low dark current and internal gain mechanism of GaN MSM photodetectors fabricated on bulk GaN substrate

摘要

Metal-semiconductor-metal ultraviolet photodetectors are fabricated on low-defect-density homoepit-axial GaN layer on bulk GaN substrate. The dislocation density of the homoepitaxial layer characterized by cathodoluminescence mapping technique is ～5 × 10~6 cm~(-2). The photodetector with a high UV-to-vis-ible rejection ratio of up to 1 ×10~5 exhibits a low dark current of ＜2 pA at room temperature under 10 V bias. The photo-responsivity of the photodetector gradually increases as a function of applied bias, resulting in a photodetector quantum efficiency exceeding 100% at above medium bias. The photo-responsivity also shows a dependence on the incident optical power density and illumination conditions. The internal gain mechanism of the photodetector is attributed to photo-generated holes trapped at the semiconductor/metal interface as well as high-field-induced image-force lowering effect.