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 approximately 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.