Saturable two-step photocurrent generation in intermediate-band solar cells including InAs quantum dots embedded in Al0.3Ga0.7As/GaAs quantum wells

We have studied detailed photocurrent generation process in the two-step photon absorption in intermediate-band solar cells including InAs quantum dots embedded in Al_0.3Ga_0.7As/GaAs quantum wells and influence of thermal carrier escape at room temperature . The photocurrent generated by the two-step photon absorption shows saturation as the inter-band excitation intensity becomes strong, and the inter-band excitation intensity showing the saturation behavior strongly depends on the inter-subband excitation intensity. To interpret this phenomenon, we carried out a theoretical simulation based on carrier dynamics considering carrier generation, energy relaxation and thermal carrier escape. The results indicate that the photocurrent saturation is caused by filling the intermediate states with electrons. The shift of the saturation point depending on the inter-subband excitation intensity is caused by the shift of the quasi-Fermi level for the intermediate states.