The role of the AlGaAs doping level on the optical gain of two-dimensional electron gas photodetectors

We compare the optical response of two modulation-doped heterojunction photodetectors with identical growth structure, differing only in the doping level of the wide band material. The larger photoresponse of the higher doped device cannot be explained as photoconductive gain because neither the transit time nor the recombination lifetimes are substantially altered by the change in doping.. Alternatively, we propose to explain the results on the basis of an optical gating effect. It is shown that proper control of the two-dimensional electron gas (2-DEG) channel population in dark conditions allows one to optimize optical responsivity and external quantum efficiency.