The effect of operating a vacuum ion gauge on carbonaceous (C) contamination of a hydrogen (H)-passivated Si surface before epitaxial growth was investigated. The dependence of C contamination on the residence time in the loading chamber, tlc, was determined with or without operating a vacuum ion gauge. The results showed that C contamination of a H-passivated surface was greatly increased by use of the ion gauge. With ion gauge operation in a vacuum of 1×10−6–1×10−7 Torr in the loading chamber, the configuration of the ion gauge and upside down-stacked wafers is shown to be a dominant factor of C contamination of the Si surface. The presence of C contaminants could be determined by observing SiC diffraction patterns using in situ reflection high energy electron diffraction (RHEED), since the C contaminants reacted with Si to produce single crystalline SiC at a temperature as high as 850 °C. The RHEED patterns demonstrated that the single crystalline SiC had a zinc-blende structure. Single crystalline SiC islands with an ellipsoidal cross section were observed by high resolution transmission electron microscopy. In the subsequent epitaxial growth of Si, a well oriented single crystalline Si layer could be grown over the SiC islands although the effect of C contamination on the electrical characteristics of the interface was not clarified. Longer tlc with the ion gauge also required a higher temperature to achieve a 2×1 reconstructed surface structure from the H-passivated Si surface.

The effect of Si+ and Ge+ source ions on surface morphology and strain relaxation of Si1−xGex (0.25≤x≤1.0) film on Si (001) substrate was investigated using potential-enhanced molecular beam epitaxy. The growth temperature ranged from 450 to 710 °C. The applied potential to the substrate was varied between −2.0 and 1.5 kV. The acceleration of a small fraction of source ions toward the substrate suppressed three-dimensional nucleation mode, and dramatically improved the surface morphology. Contrary to the negative potential, the application of a positive potential did not contribute to improving the surface smoothness of Ge on Si. For the growth of Si0.5Ge0.5 film, the surface morphology was degraded further by applying a positive potential of 1.5 kV. Si0.75Ge0.25 films grown with a negative potential of −1.6 kV relieved the strain at the much earlier stage of heteroepitaxial growth than that of conventional molecular-beam epitaxy.