Contrast effects in strained layer InGaAs/GaAs superlattices

摘要

The contrast behaviour of In_xGa_(1-x)As/GaAs strained layers for imaging under systematic row conditions where the composition sensitive g=200 reflection is precisely at the Bragg condition has been studied. The contrast behaviour of the layers as a function of x is kinematically modelled. Because of the quadratic expression in x for In_xGa_(1-x)As contrast reversal occurs at some x. The point of reversal is shown to be sensitive to the atomic scattering factors used in the calculation. The relative contributions of other factors to the layer contrast such as 1) multiple scattering, 2) inelastic scattering, 3) thin film surface relaxation effects, 4) systematic row effects, 5) thickness/absorption effects and 6) tetragonal distortion are considered.