An optical study of the lateral motion of two-dimensional electron-hole pairs in GaAs/AlGaAs quantum wells

Abstract

The authors have studied the lateral transport of electron-hole (e-h) pairs in GaAs/AlxGa1-xAs quantum wells (QWS) (0.3<or=x<or=1.0) as a function of well width, temperature and Al content in the barriers by a method based on transparent circular microstructured areas in otherwise opaque masks. In the experiment they observe an increase of the e-h-pair mobilities with both growing Al content and increasing well width. The experimental results are compared with theoretical model calculations for different scattering mechanisms such as acoustic-deformation-potential (AC), polar-optical (PO), barrier-alloy-disorder (BAL), impurity and interface-roughness (IR) scattering. For low temperatures (about 40 K<T<90 K) the increase observed in the experiment can most probably be related to efficient IR scattering. Model calculations of IR scattering were used to determine approximately the geometrical roughness parameters of the interfaces. Based on this analysis, the authors' samples investigated in this paper show average terrace heights of one monolayer, independent of well width. BAL scattering is found to affect the mobility of e-h pairs only for very narrow QWS at temperatures close to 100 K. At higher temperatures T>100 K AC scattering and PO scattering are found to dominate the scattering processes. In addition, a crossing of the theoretical electron and hole mobilities is observed for isolated BAL scattering for very narrow well widths or very low Al contents.