Effect of Metal Contacts on a GaN/Sapphire-Based MSM Ultraviolet Photodetector

Abstract

We report the fabrication of a GaN/sapphire ultraviolet (UV) photodetector (PD) with asymmetric (Pt-Ag) and symmetric (Pt-Pt) metal–semiconductor–metal (MSM) structure. The fabricated devices display Schottky behavior. Time-dependent photoresponse analysis reveals a significant enhancement in photocurrent leading to a photoresponsivity of 37 mA/W and 267 mA/W under 13 mW optical power at 5 V bias for Pt-Pt and Pt-Ag devices, respectively. Further, power-dependent measurements reveal a peak responsivity of 633 mA/W at 4mW optical power and 5 V bias for the Pt-Ag asymmetric MSM photodetector. The significant enhancement in responsivity for asymmetric MSM UV PD is ascribed to the built-in potential gradient in the GaN semiconductor, which drives a large number of charge carriers for enhanced charge collection. Further, the noise equivalent power was lowest for the Pt-Ag MSM structure, which was calculated to be 4.6 × 10⁻¹⁴ WHz^−1/2. This high performance asymmetric MSM GaN UV PD can be integrated into efficient UV PD-based applications.