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 detection of strained epitaxial layer relaxation. Strained layer superlattices (SLSs) of InGaAs/GaAs were prepared by molecular beam epitaxy. The rapid increase in the LLS signal was interpreted as increased surface roughness due to surface steps generated during InGaAs relaxation. The LLS signal was sharply peaked with respect to the azimuthal angle (the rotation angle between crystal axes and the detection axis), indicating the scattering comes primarily from alpha misfit dislocations which run parallel to the (011BAR) direction. The growth time at which the LLS signal onset occurred, together with the InGaAs growth rate, yielded the critical layer thickness, h(c). The h(c) value for SLSs of In0.17Ga0.83As/GaAs with thicknesses of 4.6/17 and 4.6/7.8 nm were 25 and 23 nm, respectively, and almost identical to values obtained for single 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 real-time.