X-RAY-SCATTERING ANALYSIS OF SURFACE-STRUCTURES PRODUCED BY VAPOR-PHASE EPITAXY OF GAAS

We have used in situ x-ray-scattering techniques to analyze surface reconstructions and ordered steps at various stages in the growth of GaAs by organometallic vapor-phase epitaxy. In contrast to an earlier report of a c(4 x 4) reconstruction, our current measurements reveal a related structure with 1 x 2 symmetry. The 1 x 2 structure is a disordered form of the c(4 x 4) reconstruction in which long-range correlations between dimer rows are preserved but dimer vacancies are located at random. Aside from reconstructions, ordered step structures were studied on samples with both high (2.2 degrees) and low (0.07 degrees) levels of miscut. Using Gaussian step-spacing distributions with widths of order the mean terrace size, a numerical model is used to reproduce measured truncation rod profiles in scans perpendicular to steps. We also use the model to follow the narrowing of the step-spacing distribution which occurs during growth. After the growth of several hundred angstroms of GaAs, truncation-rod profiles sharpen, accompanied by a shift in peak positions. The shift is due to an asymmetric weighting of the scattering from terraces of different widths: wide terraces make a greater contribution to the structure factor. For samples with a broadened distribution of step spacings, this effect results in a smaller peak splitting than that which would occur for an ideally miscut sample.