We systematically studied two-step photocurrent generation as functions of the excitation intensities for the inter-band and inter-subband transitions in an InAs/GaAs/Al0.3Ga0.7As dot-in-well (DWELL) intermediate-band solar cell.The two-step photoexcitation current shows saturation as the inter-band excitation intensity becomes strong, and we found that the inter-band excitation intensity showing the current saturation strongly depends on the inter-subband excitation intensity. To interpret the current-saturation behavior, we proposed a model and carried out theoretical simulation. Simulated results excellently reproduce the experimental observations. It has been clarified that the photocurrent saturation is caused by filling the intermediate states with electrons.Furthermore, the recombination lifetime in DWELL was pointed out to be extremely long.Our results suggest that this carrier lifetime is an important key to realize strong enhancement of two-step photoexcitation.
