Experimental study of the Γ-<i>X</i>electron transfer in type-II (Al,Ga)As/AlAs superlattices and multiple-quantum-well structures

Abstract

A detailed experimental study of the real-space \ensuremath{\Gamma}-X transfer in type-II GaAs/AlAs short-period superlattices and in type-II ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/AlAs multiple-quantum-well structures is presented. Transfer times on a subpicosecond and picosecond time scale are observed. The time constants critically depend on the thickness of the (Al,Ga)As layers, but not on the AlAs-layer thickness in the samples studied. The \ensuremath{\Gamma}-X transfer rate is determined by the spatial overlap of the \ensuremath{\Gamma} and X wave functions confined in the different layers. Intensity- and temperature-dependent measurements provide insight into the scattering mechanism. We conclude that electron--LO-phonon scattering is the dominant scattering process for samples with thick (Al,Ga)As layers (&gt;100 \AA{}). In contrast, interface scattering due to the interface mixing potential (\ensuremath{\Gamma}-${\mathit{X}}_{\mathit{z}}$ mixing) and/or due to potential fluctuations caused by interface roughness (\ensuremath{\Gamma}-${\mathit{X}}_{\mathit{x},}$y mixing) probably dominates for samples with thin (Al,Ga)As layers (35 \AA{}).