In situ detection of InGaAs strained-layer relaxation by laser light scattering

Abstract

The utility of in situ laser light scattering (LLS) to monitor molecular beam epitaxy growth of InGaAs/GaAs strained layers is demonstrated. LLS signatures were correlated with ex situ characterization by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Desorption of GaAs native oxide resulted in surface pit formation (3–10 nm depth, 30–100 nm width, density of 109–1010 cm−2) which caused a slight increase in LLS signal. Deposition of a GaAs buffer layer reduced the surface pitting, then formed a wavy surface morphology, with step deviations of ∼5 monolayers which were aligned in the (011̄) direction. InGaAs layer growth at 515 °C resulted in a rapid increase in LLS intensity, after an initial onset time, because of the increasing density and height of surface steps generated by misfit dislocations. Critical thickness was determined in situ from the LLS onset time, which depended inversely on the InGaAs composition, and was compared to equilibrium model predictions. By rotating the wafer, contributions to the LLS signal from misfit dislocations could be separated from isotropic surface roughness. Three-dimensional (island) growth occurred in films with In content above 25%. Observations of relaxation dynamics included the continuing increase of LLS signal even afer InGaAs layer growth was terminated. During GaAs cap layer growth, a decrease in the density ratio of α(011̄) to β(001) dislocations was also observed.