In Operando Quantification of Single and Multiphoton Photocurrents in GaP and InGaN Photodetectors with Phase-Modulated Femtosecond Light Pulses

Single and multiphoton absorptions in wide band gap semiconductors determine the functionality of photodetectors, lasers, and light-emitting diodes (LEDs). Although electronic structure strongly influences the different orders of multiphoton absorptions in semiconductors, it has not been feasible to quantify their contributions on the functionality of devices. A lack of proper measurement techniques has been the hurdle. Here, we present a simple and sensitive method based on the phase modulation of femtosecond pulses to quantify single-, two-, and three-photon absorptions in GaP and InGaN photodetectors. Our results show that only three-photon absorption contributes to the photocurrent in the InGaN device when excited by femtosecond pulses at 1030 nm. On the other hand, single-, two-, and three-photon absorptions have comparable contributions in the GaP detector. The three contributions have different origins: linear photocurrent is attributed to the absorption by the impurities in the doped regions, two-photon photocurrent is from the phonon-assisted indirect transition from the valence band to the conduction band minimum, and three-photon photocurrent is from the direct transition to the conduction band. We also demonstrate that the method can be applied to image the heterogeneity of multiphoton photocurrent in devices. Our work could be adapted for "in operando" characterization of optoelectronic systems.