Optically induced density depletion of the two-dimensional electron system in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterojunctions

We report measurements of optically induced density depletion of the two-dimensional electron system formed at the interface of a GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterojunction with a δ-doped layer of Be acceptors in the GaAs 250 Å from the interface. Our measurements show that at low laser power the depletion effect is controlled by the recombination of two-dimensional electrons with photoexcited holes that have become bound to the Be acceptors. The point at which all the Be acceptors in the sample have been neutralized by photoexcited holes is indicated by the sudden appearance of free holes in the GaAs, which then control the density depletion in the high-power regime. We present a comprehensive dynamic model of the depletion effect that includes both regimes, and calculate the densities and mobilities of the carriers involved in the process.