Study Of High Deep-Ultraviolet Quantum Effciency GaN-based Photodetectors

GaN-based semiconductors are very attractive for fabricating highly sensitive ultraviolet (UV) photodetectors (PDs) owing to their wide direct bandgap, terrific chemical and physical stability, and increasingly improved material growth/processing technologies. These PDs have wide applications in the fields of missile plume sensing, flame detection, chemical/biological agent sensing, environmental monitoring and covert space-to-space communication. Over the last few years, various types of GaN-based PDs have been demonstrated with promising performance including photoconductors, metal-semiconductor-metal PDs, Schottky barrier PDs, and p-i-n PDs. Among these structures, p-i-n PDs draw particular interest for their advantages of low dark current, relatively high speed, and high stability. However, due to the strong UV light absorption by the p-GaN contact layer, top illuminated GaN p-i-n PDs commonly suffer from low quantum efficiency, especially in the deep-UV wavelength range.In this work, in order to improve quantum efficiency, especially in the deep-UV wavelength range, of GaN p-i-n PDs, we fabricated a GaN UV p-i-n PD with40nm thin p-GaN contact layer on a sapphire substrate by MOCVD. The PDs exhibit enhanced quantum efficiency especially in deep-UV wavelength range. The PD shows good rectification behavior and low dark current in pA level for reverse bias up to-10V. Under zero bias, the maximum quantum efficiency of the PD at360nm is close to59.4%with a UV/visible rejection ratio more than4orders of magnitude. Even at a short wavelength of280nm, the quantum efficiency of the PD is still around47.5%, which is considerably higher than that of a control device with thicker p-GaN contact layer. The room temperature thermal noise limited detectivity of the PD is calculated to be～4.96×1014cm Hz1/2W-1, which is of the same order of magnitude than the highest detectivity performance reported for GaN p-i-n UV PDs.