Mextram modeling of Si/SiGe heterojunction phototransistors

To integrate the phototransistor into the receiver circuit for optical communication, not only the compatible process is pre-requisite, but also the device model is required for circuit simulation. The designed nkT base current (depletion region recombination current at B-E junction) can increase the bandwidth of the phototransistor and provide a possible bias margin for avalanche gain. Therefore, a modified Mextram model is proposed for the heterojunction phototransistors (HPT) simulation. The common emitter output characteristics in a log I_c scale have to be modeled by modified Mextram model. We concluded that the Mextram model is suitable for HPT modeling because the nkT base recombination current can increase the HPT speed.