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We have examined the influence of strain relaxation on the excitonic recombination and diffusion in In0.2Ga0.8As/AlxGa1−xAs quantum‐well (QW) samples designed for high‐electron‐mobility transistors, using spectrally and spatially resolved polarized cathodoluminescence (CL). Six molecular‐beam epitaxial grown samples, with varying channel thicknesses ranging from 75 to 300 A, were examined at various temperatures between 87 and 300 K. An increase in misfit dislocation density occurred with increasing channel thicknesses and resulted in changes in the dark line defect (DLD) density, polarization anisotropy, QW excitonic luminescence energy, and luminescence activation energy, as observed in CL. The influence of misfit dislocations on the ambipolar diffusion of excess carriers in a direction parallel to the dislocation line, in varying proximity to the DLDs, was examined with a CL‐based diffusion experiment. The temperature dependence of the CL imaging was examined, enabling a study of the spatial variation ...

Local variations in the optical properties of thick In0.13Ga0.87As films grown on GaAs(001) substrates misoriented toward {111} planes have been studied with polarized and spectrally‐resolved cathodoluminescence (CL) imaging. The degree of anisotropic relaxation and density of dark line defects (DLDs) in CL was found to depend on the choice of the substrate miscut orientation. An enhanced anisotropy in DLD density and strain relaxation was found for a misorientation towards (111)A relative to that for a misorientation towards (111)B. Local variations and spatial correlations in polarization anisotropy, band‐gap energy shifts, luminescence efficiency, and defect‐induced long‐wavelength luminescence were examined.

Strained, coherent InAs islands were grown on GaAs (100) planar substrates by molecular‐beam epitaxy (MBE). These coherent islands were buried under GaAs cap layers grown by MBE and migration enhanced epitaxy at low temperature (∼ 400 °C), the latter case exhibiting an order of magnitude stronger photoluminescence (PL). The PL and PL excitation spectra reveal the discrete nature of the density of states of three‐dimensionally confined electronic states in the islands. The possibility of placing InAs on a regular array of prepatterned square mesas, size‐reduced via buffer layer growth to a ≤150 nm mesa top, was explored. The InAs on mesas with sub‐100 nm lateral dimensions is found to have an enhanced critical thickness for two‐dimensional to three‐dimensional island morphology transition, going from ∼1.8 monolayers (ML) for growth on planar substrate to ≥5 ML for 70 nm mesas. Spectrally and spatially resolved cathodoluminescence studies show these InAs volumes to be optically active.

The effects of excess carrier generation on excitonic absorption phenomena in nipi‐doped In0.2Ga0.8As/GaAs multiple quantum wells (MQWs) was examined using a novel technique called electron beam‐induced absorption modulation imaging. The nipi‐doping induced barrier height is determined by measuring the frequency response of the absorption modulation as a function of temperature and employing a model which is based on thermal excitation of carriers in the limit of Boltzmann statistics. Spatial steps in the absorption modulation which correlate with the positions and orientation of dark line defects imaged in cathodoluminescence are observed. These results indicate the existence of defects in the MQWs which impede the ambipolar diffusive transport of the spatially separated electron‐hole plasma.