EFFECT OF INTERFACE DEFECT FORMATION ON CARRIER DIFFUSION AND LUMINESCENCE IN IN0.2GA0.8AS ALXGA1-XAS QUANTUM-WELLS/

We have examined the influence of strain relaxation on the excitonic r ecombination and diffusion in In0.2Ga0.8As/AlxGa1-xAs quantum-well (QW ) samples designed for high-electron-mobility transistors, using spect rally and spatially resolved polarized cathodoluminescence (CL). Six m olecular-beam epitaxial grown samples, with varying channel thicknesse s ranging from 75 to 300 Angstrom, were examined at various temperatur es between 87 and 300 K. An increase in misfit dislocation density occ urred with increasing channel thicknesses and resulted in changes in t he dark line defect (DLD) density, polarization anisotropy, QW exciton ic luminescence energy, and luminescence activation energy, as observe d in CL. The influence of misfit dislocations on the ambipolar diffusi on of excess carriers in a direction parallel to the dislocation line, in varying proximity to the DLDs, was examined with a CL-based diffus ion experiment. The temperature dependence of the CL imaging was exami ned, enabling a study of the spatial variation of the activation energ ies associated with thermal quenching of the GaAs/Al0.25Ga0.75As multi ple QW and In0.2Ga0.8As QW luminescence. The CL intensity exhibits an Arrenhius-type dependence on temperature and is controlled by thermall y activated nonradiative recombination. The activation energies for bo th the In0.2Ga0.8As QW and Al0.25Ga0.75As MQW luminescence are found t o vary spatially in close proximity to the misfit dislocations. We hav e utilized a new approach to obtain 2D images of the activation energi es. The influence of the strain relaxation on the polarization and ene rgy of the In0.2Ga0.8As QW excitonic luminescence was examined with li nearly polarized CL and CL wavelength imaging. A strain-induced modifi cation of the luminescence energy and an increase in the polarization anisotropy was measured near DLDs. Thus, we find that certain DLDs exh ibit significant polarization and energy variations in their optical p roperties, in addition to their more familiar nonradiative behavior. ( C) 1996 American Vaccum Society.