Influences of MBE growth processes on photovoltaic 3-5 μm intersubband photodetectors

The asymmetric photoresponse and dark current of GaAs/AlAs/Al_0.3Ga_0.7As 3-5 μm intersubband photodetectors is examined both experimentally and through simulations. The intended doping position is varied to determine the importance of dopant redistribution on the detector characteristics. Growth interruptions were introduced to determine the importance of inequivalent heterointerface roughness. An improved segregation model is developed which includes the influence of an incident doping flux. The growth-rate limited silicon incorporation coefficient during GaAs growth was determined as a function of growth temperature and growth rate from published SIMS profiles. The conduction band bending in these detectors was calculated semiclassically to estimate the applied voltage necessary to compensate the doping asymmetry. Si segregation explains 75-100% of the experimentally observed compensating voltage, without the introduction of fitting parameters. The remaining portion of the compensating voltage is largely due to asymmetric interface roughness. Growth interruptions reduce the linewidth of the QW intersubband absorption and also the detector responsivities, in apparent agreement with theoretical predictions