Selective growth of SiGe quantum dots on hydrogen-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 ∼400 °C while those from monohydride-terminated (111) facets remain stable up to 650 °C. Thus, for growth carried out in the temperature range of 400–650 °C, the adsorption of hydride molecules occurs only on the sites that have been previously terminated by dihydrides, i.e. free of hydrogen. We show that SiGe islands with size being reduced down to −200 Å can be achieved by using this new approach.