Superlinear photoluminescence and vertical transport of photoexcited carriers in modulation-doped heterojunctions

摘要

Abstract: We verify the validity of the optical characterization of the 2D electron gas confined in modulation doped (GaAl)/As/GaAs heterojunctions designed for both high electron mobility devices. The properties of the 2D electron gas are evaluated from the magneto photoluminescence and the microwave influenced photoluminescence detected on the GaAs excitons in the flat band region. We evaluate the electron density and mobility from the oscillation of the photoluminescence intensity in a magnetic field, and the effective mass from the resonant change of the PL intensity under additional microwave radiation. We attribute these non-linear optical properties to the vertical transport and the bimolecular exciton formation of photoexcited carriers. We proved these specific transport and exciton formation processes by time-resolved photoluminescence experiments, where an extremely long exciton formation time and a strong signal of anti-stokes emissions under resonant excitations are observed. Furthermore, we realized a significant amplification of the photoluminescence intensity by exciting the heterojunction with two temporarily delayed laser pulses. The amplification of the luminescence intensity reflects unambiguously the recycling through the bimolecular exciton formation of the photo-excited carriers accumulated in the flat band region after vertical transport.!28