Optical investigations on the mobility of two-dimensional excitons in GaAs/Ga1−xAlxAs quantum wells

Abstract

By time-of-flight studies, the lateral transport of two-dimensional excitons in GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As quantum wells is studied with a very high spatial resolution (∼0.1 μm) provided by laterally microstructured masks. The motion of the excitons is investigated for different quantum-well widths over a wide temperature range and can be described entirely by isothermal diffusion. In particular, at low temperatures the diffusivity strongly decreases with decreasing well width. The low-temperature mobilities are found to be mainly determined by interface-roughness scattering. In the range where acoustic-deformation-potential scattering is dominant, the mobility of the excitons as a function of temperature and well width is found to agree with the corresponding theoretical mobility limits. The excitonic scattering condition describes the experiment much better than the ambi- polar scattering condition. The comparison of experimental results and calculated mobility limits shows that barrier-alloy disorder scattering significantly affects the mobilities of excitons only in narrow GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Al}}_{\mathrm{x}}$As quantum wells.