The role of p-GaN layer thickness for the evaluation of high-performance and ultrafast GaInN/GaN multiple quantum wells UV photodetectors

Abstract

To improve the performance of GaInN/GaN multiple quantum wells (MQW) ultraviolet photodetectors (UV-PDs), the thickness of p-GaN layer plays an important role. Thereby, to see the impact of p-GaN layer thickness on epilayer quality and device performances, in the present work, we fabricated two different sets of GaInN/GaN MQW-based UV-PDs by varying the thickness of p-GaN layer and examined their epilayer quality and device performances by employing various adequate measurements. Due to increase of p-GaN layer thickness from 125 nm (PD1) to 250 nm (PD2), the density of threading dislocations increases which in turn declines the photocurrent (Ip) and hence, the external quantum efficiency (EQE) in the higher excitation regime (<372 nm). On the other hand, above 372 nm, the values of Ip and EQE in PD2 are higher compared to PD1, indicating the length of photo-absorption layer is improved. Interestingly, PD2 exhibits the widening of the spectral sensitivity towards the higher wavelength regime. Moreover, the temporal photo-response measurements at different optical powers, bias voltages, and switching frequencies (wavelength of the light source = 385 nm) reveal that PD2 has relatively better performance over PD1. These results imply that the separation of photoexcited electron-hole pairs is easier in PD2 than PD1. The faster carrier separation process in PD2 is ascribed to the exacerbated built-in potential in the heterojunction as confirmed via capacitance-voltage analysis. Finally, current–voltage measurements suggest that the series resistance in PD2 increases due to increase of total film thickness.