HYPERFINE INTERACTIONS OF IN-111-]CD-111 PROBE ATOMS ON GAAS(111)B RECONSTRUCTED SURFACES

We have used In-111 --> Cd-111 perturbed-angular-correlation (PAC) spe ctroscopy to measure hyperfine interactions at surface sites on two mo lecular-beam-epitaxy-grown GaAs (111)B (As-terminated) reconstructed s urfaces. The PAC measurements performed on the 2 x 2 reconstructed sur faces show two well-defined nuclear electric-quadrupole interactions t hat occur at two inequivalent Ga-sites on the surface. The measurement s performed on the root 19 x root 19 R 23.4 degrees reconstructed surf aces show primarily one well-defined interaction to which corresponds a large and asymmetric EFG, in which the EFG z-axis is oriented essent ially perpendicular to the surface. Annealing experiments were perform ed to convert one reconstruction to the other and then to reconvert it back to the original reconstruction, e.g., 2 x 2 --> root 19 x root 1 9 R 23.4 degrees --> 2 x 2. The PAC measurements that followed each an nealing step show the characteristic frequencies for each reconstructi on. This result indicates that these probe sites are thermodynamically stable. In this report, we present a brief description of the experim ent and, as an example, one series of measurements that illustrates th e results of an extensive investigation, which reports the first measu rements of group-III bonding symmetries on a compound III-V semiconduc tor surface.