Abstract
High quality homoepitaxial growth of Si on Si(111) mediated by an overlayer of Pb is shown to occur at 280 C, far below the temperature required for growth of Si of similar quality on bare Si(111). Films of unlimited thickness can be obtained with excellent crystalline quality, as revealed by Rutherford backscattering spectrometry (RBS) ion channeling measurements ( Xmin = 2.9% ). A distinct range of Pb coverage [ 0.8 - 1.0 monolayer (ML) ] results in the best quality epitaxy, with no measurable amount of Pb trapped at either the interface or within the grown films. Cross-sectional transmission electron microscopy (TEM) reveals that in films grown with Pb coverages below and above the optimum range, the predominant defects are stacking faults on (111) planes and Pb inclusions, respectively. Heteroepitaxial growth of Ge on Si(111) mediated by Pb overlayers is shown to result in Ge island formation. Although RBS measurements are not as meaningful for films with large 3-dimensional islands, TEM reveals that at substrate temperatures of 340 - 400 C and Pb coverages ranging from 0.3 - 2.5 ML, 3-dimensional Ge islands form after growth of several hundreds of Angstroms of flat epitaxial Ge layers. A general growth mechanism is proposed which attempts to explain the observed effects of the Pb mediating overlayers for the homoepitaxial and heteroepitaxial systems. The proposed mechanism also attempts to encompass the growth phenomena reported by several authors who have used other elements as mediating overlayers in similar systems.