CARRIER CAPTURE IN QUANTUM WELLS AND ITS IMPORTANCE FOR AMBIPOLAR TRANSPORT

The transmission, reflection, and capture probabilities of carriers in a quantum well heterostructure are calculated including the decrease of the current density across the well and the decay of phase coherence, which reduces the resonant structure of the transmission probability. These probabilities connect the carrier distribution functions on both sides of the well. We introduce 'interface velocities', which serve as boundary conditions for the diffusion equation. The velocities of electrons and holes are, in general, quite different. Analogous to the ambipolar diffusion coefficient ambipolar interface velocities are calculated from the quantities for both carrier types. For typical sample dimensions and carrier densities the ambipolar calculation is in very good agreement with a two-component calculation. In very small samples at low densities, however, the results differ. It is demonstrated that a unique determination of the diffusion coefficient and the interface parameters requires measurements at different transport distances.