Optical studies of vertical ambipolar transport and interface recombination velocities in GaAs/${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$As double-quantum-well heterostructures

We present a detailed experimental and theoretical study of vertical ambipolar transport in semiconductor heterostructures. A high-resolution time-of-flight method using two vertically separated quantum wells of different well widths is applied to probe the carrier transport perpendicular to the heterointerfaces. By a numerical simulation the ambipolar diffusivities as well as surface and interface recombination velocities in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As structures are determined. This paper emphasizes the importance of surface and interface recombination for the analysis of the transport data. Alloy-disorder scattering is found to limit the ambipolar mobilities between 40 and 120 K in the ${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$As barriers with acoustic-deformation-potential and polar-optical scattering participating above 120 K. In addition to the transport properties, we also obtain information on carrier capture from the barrier layers into the quantum well as a function of temperature.