Laser light scattering detection of InGaAs strained layer relaxation during molecular-beam epitaxial growth

Abstract

The in situ detection of strained layer relaxation in the InGaAs/GaAs system using laser light scattering (LLS) is reported. Samples were prepared by molecular-beam epitaxial deposition of InGaAs at 515 °C, and were characterized ex situ with x-ray diffraction, transmission electron microscopy, and atomic force microscopy. The LLS signal rapidly increased after an onset period which depended on the InGaAs composition. Azimuthal rotation [about the (100) surface normal] was a useful diagnostic for analyzing the contributions to the LLS signal. For InxGa1−xAs films with x<0.25, the LLS signal was strongly peaked toward wafer-plane directions normal to the [011̄] or [011] axes, due to scattering from α or β misfit dislocations, respectively. Nearly isotropic scattering was observed for films with In content above 25%, indicating three-dimensional growth which followed an initial two-dimensional growth period. The results were compared to model predictions of the critical layer thickness. Dynamic effects of the relaxation were observed, in which the LLS signal continued to increase after InGaAs layer growth had terminated. It was also observed that the density ratio of α to β dislocations changed with GaAs cap layer growth. These results demonstrate the utility of LLS for in situ monitoring of layer relaxation and determination of critical thickness.