Effects of Zn Doped Mesa Sidewall on Gain Enhanced InGaAs/InP Heterobipolar Phototransistor

The excellent detectability of the gain enhanced InGaAs/InP heterobipolar phototransistor (GE-HPT) is demonstrated and attributed to a reduction in the reverse leakage current at the base-collector junction and the enhancement of current gain at the emitter-base junction achieved by using a current blocking structure with a Zn doped mesa sidewall. The common emitter grounded current gain agrees well with the photo-conversion efficiency of several tens of thousands of A/W at incident optical powers in the hundred nanowatt to sub-picowatt range over several orders of magnitude. The deep mesa structure in the GE-HPT is also effective in ensuring superior isolation of better than 25 dB between adjacent arrays.