Effects of impurity band on multiphoton photocurrent in GaN and InGaN photodetectors

GaN and InGaN are prototypical wide band-gap semiconductors with application in light-emitting diodes, photo-detectors, high-power electronics, photonics, and opto-electronics. Despite their popularity, defects and impurities compromise functionality of devices made out of them. Here, we investigate how the impurities and defects affect multiphoton photocurrents in GaN and InGaN-based photodetetors using intensity-modulated femtosecond laser pulses. Photocurrent from InGaN detector shows nearly perfect quadratic dependence on excitation intensity when excited by photons at 2.4 eV, while that in GaN detector shows cubic and higher order dependence. We also observe yellow luminescence from both the detectors that show sub-quadratic dependence on excitation intensity. Highly nonlinear photocurrent from GaN is ascribed to absorption of additional photons by long-lived electrons in traps and impurity bands. Our investigation indicates that InGaN can serve as a superior material for multiphoton absorption and high-power optoelectronics due to the absence of long-lived trapped charges, while GaN, which suffers from absorption by trapped electrons and impurity bands, must be used with caution in such applications.