INSITU DETECTION OF RELAXATION IN INGAAS GAAS STRAINED-LAYER SUPERLATTICES USING LASER-LIGHT SCATTERING/

We report the use of laser light scattering (LLS) for the in situ dete ction of strained epitaxial layer relaxation. Strained layer superlatt ices (SLSs) of InGaAs/GaAs were prepared by molecular beam epitaxy. Th e rapid increase in the LLS signal was interpreted as increased surfac e roughness due to surface steps generated during InGaAs relaxation. T he LLS signal was sharply peaked with respect to the azimuthal angle ( the rotation angle between crystal axes and the detection axis), indic ating the scattering comes primarily from alpha misfit dislocations wh ich run parallel to the (011BAR) direction. The growth time at which t he LLS signal onset occurred, together with the InGaAs growth rate, yi elded the critical layer thickness, h(c). The h(c) value for SLSs of I n0.17Ga0.83As/GaAs with thicknesses of 4.6/17 and 4.6/7.8 nm were 25 a nd 23 nm, respectively, and almost identical to values obtained for si ngle InGaAs layers. The observed values of h(c) are greater than those calculated using the standard force-balance model. Dynamic effects of dislocation propagation and surface smoothing were also observed in r eal-time.