ACCURATELY DETERMINING THE COMPOSITION AND THICKNESS OF LAYERS IN A GAAS INGAAS SUPERLATTICE/

The layer thicknesses and composition of molecular beam epitaxy grown four period 200 angstrom/100 angstrom GaAs/InGaAs superlattice structu res with nominal indium concentrations of 10%, 15%, and 20% were deter mined by transmission electron microscopy, Rutherford backscattering s pectroscopy, double crystal x-ray diffraction (DXRD), photoreflectance (PR), and photoluminescence (PL). The results show that the indium co ncentration obtained by DXRD is a little low and that obtained by PR a nd PL is a little high, and that the discrepancies are larger for the larger indium concentrations. We show that both discrepancies can be a ccounted for by relaxation of the lattice, elastic relaxation as repre sented by a radius of curvature, and/or plastic deformation as represe nted by mismatch of dislocations. For the case of elastic relaxation t he tetragonal distortion is less than it would be if the sample were p erfectly pseudomorphic. The fractions by which it is reduced for the 1 0%, 15%, and 20% samples was 0.91, 0.86, and 0.77 as determined by DXR D and 0.80, 0.78, and 0.85 as determined by PR/PL.