Metal-Induced Reconstructions on Semiconductor Surfaces

Scanning tunneling microscopy (STM) has been used to study the surface morphology induced by In, Ga, and Sn overlayers on Si(100) and Si(311) surfaces. STM and low-energy electron microscopy (LEEM) were used to study the surface morphology of Pb overlayer grown on Si(100) -(2 x 1). Reconstructions on clean alpha -SiC(0001) and alpha-SiC(0001) surfaces and those induced by deposition of Ti were also studied. We found that deposition of In produced step bunching and faceting on vicinal Si(100) surface. At coverages >=1 ML, the original step direction of (01 1) changed to a zig-zag along low-index (010) and (001) directions, and the bunched steps became {130} facets. At annealing temperatures >=550^ circC, the {130} facets disappeared and the bunched steps were restored with meandering step directions. For the case of Pb adsorption on Si(100)-(2 x 1) surface, surface reconstructions of (2 x 2), c(4 x 8), (2 x 1), and c(4 x 4) were observed as Pb coverages increased from 0.5 to 1.5 ML. After the appearance of the c(4 x 4) phase, Pb islands with threefold-symmetric (111) orientation were observed on the twofold or fourfold-symmetric Si(100) surface. Both Sn and Ga adsorption on Si(100)-(2 x 1) and Si(311)-(3 x 2) surfaces induced complex surface morphologies when the coverage exceeded 1 ML. Rectangular and square depressions shaped like inverted pyramids were formed at Ga coverage above 1 ML. The walls of the inverted pyramids were (311). Deposition of Sn on Si(100) at coverages exceeding 2 ML also produced (311) facets, but they formed the faces of long parallel and orthogonal prisms, giving rise to a large scale maze-like structure on the surface. Deposition of Ga on the Si(311)-(3 x 2) surface produced ordered (211) and (611) facets at coverage above 1 ML. On the other hand, deposition of Sn on Si(311)-(3 x 2) did not produce any facet. Instead, layer-by-layer growth of (1 x 1) pseudomorphic Sn was observed on the Si(311) surface up to 6 ML. Ge growth on Si(100) surface is Stranski-Krastanov type, and the transition from 2D to 3D growth is mediated by a number of intermediate growth morphologies. These morphologies can be changed by the introduction of a surfactant such as Pb and Sn during the growth process. At Ge coverage below 3 ML, growth of Ge on surfactant-terminated surfaces resulted in an incomplete layer-by-layer mode compared to the step-flow mode without surfactant. When Ge coverage exceeded 4ML, surface morphology changed from elongated islands with (105) facets to almost square islands with (311) facets when Sn was the surfactant. For clean alpha-SiC(0001) and alpha-SiC(000 1) surfaces, ( surd3 x surd3) and (3 x 3) reconstructions were observed after annealing the surfaces in a Si flux at temperatures from 850 to 950 ^circC. A (9 x 9) reconstruction was observed only on Si-terminated face. Deposition of Ti onto the Si-terminated (9 x 9) and C-terminated (3 x 3) surfaces resulted in the formation of Ti clusters without any reaction between Ti and alpha -SiC at room temperature. (Abstract shortened by UMI.).