Abstract
Photoinduced charge redistribution processes in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well structures are studied using steady-state photoluminescence, photoreflectance, and scanning spreading resistance microscopy with an additional illumination. It is shown that an above-barrier optical pumping leads to the accumulation of electrons in the quantum wells. The resulting concentration of excess electrons in the quantum wells is several orders of magnitude higher than the concentration of photoexcited electron-hole pairs. These excess electrons induce broadening of excitonic resonances and, furthermore, cause an enhancement in the photoluminescence quantum yield and an increase in the relative intensity of the bound-exciton emission line. The additional below-barrier illumination at temperatures about 100 K leads to a decrease in the excess electron concentration in the quantum wells. The observed phenomena are explained in terms of a simple model considering the formation of a barrier in the conduction band near the ZnMgSSe/GaAs heterointerface.
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