Carrier escape mechanisms from GaAs/AlxGa1−xAs multiple quantum wells in an electric field

We have studied the vertical transport mechanisms in GaAs/AlxGa1−xAs multiple quantum wells in electric fields from the temperature dependence of the photocurrent. On heating from 10 K, we observed a decrease in the photocurrent up to ∼100 K, followed by a steady increase up to room temperature. The decrease is shown to be consistent with charged-impurity-assisted nonresonant tunneling which varies as T−1/2 in two dimensions, while the increase is consistent with thermal emission. The low field activation energy measured in a sample with x=0.33 is consistent with the thermal emission of heavy holes.