Impact of surface recombination on the responsivity of GaAs- and InP-based heterojunction photo-transistors

We outlined a detailed analytical model for responsivity of heterojunction phototransistors (HPTs). The model has been used to analyse responsivity of Al_0.3Ga_0.7As/GaAs and InP/In_0.47Ga_0.53As HPT devices. Detailed analysis on surface recombination was performed and it has been observed that the recombination was higher for graded GaAs-based devices compared to InP-based devices lattice matched to In_0.47Ga_0.53As. In addition, Surface recombination parameter was higher at smaller incident wavelengths for both material systems and a detailed analysis on this parameter is provided in this work.