RAMAN-SCATTERING VERIFICATION OF NONPERSISTENT OPTICAL CONTROL OF ELECTRON-DENSITY IN A HETEROJUNCTION

We report electronic Raman scattering measurements of the plasmon mode in a single GaAs/AlGaAs heterojunction, with a δ layer of acceptors in the GaAs buffer a well-defined distance from the interface. Under illumination above the band gap of the AlGaAs barrier, a dynamic charge-transfer effect occurs in which the quasi-two-dimensional electron concentration of the hetrojunction decreases. From Raman measurements of the plasmon mode we directly determine the change in carrier concentration with excess illumination. We obtain a time of τ=120 ps for the transfer of electrons from the AlGaAs barrier into the two-dimensional channel.