In-situ strain measurement during epitaxy of InP based materials

We have developed an instrument to measure wafer curvature during epitaxial growth in rotating disk reactors. This instrument uses a high speed, position sensitive, laser reflectometer to accurately measure the substrate's radius of curvature. The instrument has been used to measure ternary compound lattice-mismatch during growth. Agreement within 60 ppm was found between strains extracted from in-situ curvature measurements and the ex-situ measured strain determined by high-resolution x-ray diffraction. Discrepancy between extracted strains for two samples was explained by the onset of pseudomorphic strain relaxation and confirmed through Hall mobility data. A correlation between Hall mobility and strain of nearly lattice-matched InGaAs on InP demonstrated the importance of in-situ strain control at growth temperature. A maximum mobility was obtained with an at growth temperature strain of 375 ppm (compressive) relative to the InP substrate and not at perfect lattice-matching conditions.