OPTICAL STUDIES OF VERTICAL AMBIPOLAR TRANSPORT AND INTERFACE RECOMBINATION VELOCITIES IN GAAS/AL0.5GA0.5AS 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/Al(x)Ga(1-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 Al0.5Ga0.5As 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.