Spectral Response Modelling of Heterojunction Phototransistors for Short Wavelength Transmission

An accurate spectral response model for phototransistors has been proposed. The model is based on the calculation of photogenerated carriers through absorption in base, collector and sub-collector regions of phototransistor. Absorption pattern in AlGaAs/GaAs heterojunction phototransistors has been analysed and discussed using the proposed model. Collection efficiency, being strictly a geometry and wavelength dependent parameter, is not considered unity unlike all the precedents and its importance is highlighted. With the aid of the absorption model, absolute responsivity of a phototransistor is predicted for the first time. Power absorption profile and quantum efficiency have also been modelled. The analysis is performed for short wavelength transmission and the measurements corroborate the simulated results.