Fabrication of SiGe quantum dots: a new approach based on selective growth on chemically prepared H-passivated Si(100) surfaces

We report, in this paper, on a new method to produce SiGe quantum dots on Si(100) surfaces. Starting from the fact that the adsorption of hydride molecules (SiH4, GeH4) requires free adsorption sites on the surface, the basic idea of our approach is to limit the number of sites for molecular adsorption. We show that etching of Si(100) surfaces in ammonium fluoride (NH4F) solution initially produces a flat and dihydride-terminated Si(100) surface and that longer etching leads to the formation of microscopic (111) facets which are regularly distributed along the surface. Hydrogen atoms are found to desorb completely from surface dihydrides at similar to 400 degrees C while those from monohydride-terminated (111) facets remain stable up to 650 degrees C. Thus, for growths carried out in the temperature range of 400-650 degrees C, the adsorption of hydride molecules occurs only on the sites that have been previously terminated by dihydride species, i.e. free of hydrogen. Compared with islands formed by the strain-induced growth mode transition, we demonstrate, by using this new approach, that SiGe islands with better uniformity and much smaller sizes (down to similar to 200 Angstrom) can be achieved. (C) 1998 Elsevier Science S.A. All rights reserved.