The effect of submonolayer Sn δ-doping layers on the growth of InGaAs and GaAs

We have studied the effect of Sn coverage on the growth of GaAs and strained InGaAs on GaAs (001) by reflection high-energy electron diffraction (RHEED). Upon deposition of fractional monolayer (ML) amounts of Sn on the GaAs (001) surface, the (2x4) reconstruction disappeared and the diffracted beam intensities decreased. However, there was no change in the width of the beams nor was there an increase in the diffuse scattering - indicating an epitaxial Sn or tin - arsenide formation. This submonolayer coverage was found to enhance the layer-by-layer growth of GaAs and was found to remain at the surface longer than previously predicted. Most dramatically, strong beats in the RHEED intensity oscillations during GaAs growth were observed at a Sn coverage of ∼0.3 ML. The growth of GaAs on a vicinal (001) surface after the deposition of Sn, was found to order the step terrace lengths and to reduce the meandering of the steps. The vicinal (001) surface oriented toward [110] ultimately ordered more than the one oriented toward [110]. For In_xGa_1-x As with x = 0.36 or 0.54, the transition between the two-dimensional and three-dimensional growth modes was found to be independent of the Sn coverage. This last result indicates that at these mole fractions and under the growth conditions used here, Sn does not appear to act as a surfactant for the growth of InGaAs.