AMBIPOLAR DIFFUSION AND CARRIER LIFETIME MEASUREMENTS IN ALL-BINARY (INAS)2(GAAS)5 STRAINED QUANTUM-WELLS GROWN ON GAAS

The in-well ambipolar diffusion coefficients and carrier lifetimes in ordered all-binary quantum wells, composed of (InAs)2(GaAs)5 short-per iod strained-layer superlattices (SPSLSs) grown on 001!-oriented GaAs substrates, are measured using picosecond optically induced transient grating and pump-probe techniques. Quantum wells containing SPSLSs ma y be expected to exhibit higher in-plane hole mobilities compared to I nGaAs ternary alloy quantum wells because of a larger average indium c ontent and reduced disorder scattering in the SPSLS structures. The re sults obtained in the SPSLSs are compared to those obtained in InGaAs alloy quantum wells of comparable well width and confinement energies. This indicates that, for a given SPSLS and its equivalent alloy, the ambipolar diffusion coefficients are comparable while the carrier life times in the SPSLSs are longer. The longer carrier lifetimes in the SP SLSs suggest that these binary structures possess fewer nonradiative r ecombination centers than the alloys. The absence of a dramatic improv ement in the transport properties, however, may indicate that imperfec t interfaces in the SPSLSs may be offsetting their possible advantages , in spite of the fact that optical measurements in the SPSLSs indicat e high quality and x-ray and transmission electron microscopic measure ments demonstrate the binary nature of these structures.