Investigation into epitaxial growth optimization of a novel AlGaN/GaN HEMT structure for application in UV photodetectors

Abstract

In this work, a novel ultraviolet (UV) photodetector (PD) based on AlGaN/u-GaN/p-GaN/u-GaN heterojunction high electron mobility transistor (HEMT) has been developed. This HEMT epilayer is grown using the metal-organic chemical vapor deposition (MOCVD) technique, and the growth parameters, including the AlGaN growth temperature, preheating temperature of the p-GaN layer, and NH₃/N₂ flow rate, are optimized to improve the quality of the epilayer. The optimized epilayer exhibits a flat surface with a root mean square value of 0.146 nm and low dislocation density. The p-GaN thickness in epitaxial wafers has a significant influence on electrical and UV photoresponse. With a p-GaN of 1 µm, the UV PD demonstrates a significant switching ratio and transconductance of 10⁷ and 127.3 mS mm⁻¹, respectively. Acting as a UV PD, it also exhibits a high light on/off ratio (I_light/I_dark) of 6.35 × 10⁵, a high responsivity (R) of 48.11 A W⁻¹, and a detectivity (D*) of 6.85 × 10¹² Jones under 365-nm UV illumination with light power density of 86.972 mW cm⁻². The high-performance HEMT and UV detectors, which incorporate p-GaN etchless technology, have been refined through advancements in epitaxial growth and structural design. These improvements solidify the groundwork for large-scale manufacturing of UV communication systems and laser diodes.