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Abstract: In this work, the growth of germanium by ultrahigh vacuum chemical vapor deposition on a 0.6nm thick SiO2 layer formed on Si(001) is investigated by in situ reflection high-energy electron diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy. Because Ge does not grow from germane on SiO2, nucleation sites were created by exposure of the surface to SiH4 at 650°C prior to the Ge deposition, which is initiated at 600°C. The first stage of Ge growth proceeds via the formation of dots that exhibit the same crystalline orientation as the Si substrate. They are assumed to grow from small apertures opened in the silica layer due to the reduction of SiO2 by Si. For further deposition time, {111}- and {113}-facetted Ge crystals are formed and the growth remains monocrystalline. The so-formed Ge crystals are found to be completely relaxed and contain some emerging defects, identified as stacking faults. No misfit or threading dislocations are observed. Consequently, the interface between Ge and the SiO2 layer remains perfectly sharp and free of defects. This relaxation without misfit dislocation is due to SiO2 layer which acts as a buffer layer that prevents the Si substrate from imposing its lattice parameter on the Ge crystal. [Copyright &y& Elsevier]

Abstract: Relaxed germanium was deposited following a low temperature–high temperature procedure by ultrahigh vacuum chemical vapor deposition in Si trenches opened through a SiO2 mask. The resulting growth is selective, the germanium fills the Si trenches and evolves towards a roof-shaped morphology limited by (001), {113} and {111} facets. The evolution in height of the Ge structure depends on the trench width, and can be understood by considering a growth rate in the 〈113〉 direction equal to 22% of that measured along the 〈001〉 axis. At last, a surprisingly strong Ge diffusion under the SiO2 mask was revealed by selective chemical etching. Such a phenomenon was unexpected because no diffusion through the Si/Ge interface was previously observed on plain wafer. [Copyright &y& Elsevier]

We have investigated the formation of Ge quantum dots (QDs) in SiO2/Si(0 0 1) windows prepared either by partial thermal desorption of an ultra-thin oxide layer, or by standard electron beam lithography. Prior to Ge growth, we studied the growth of a silicon buffer. It was shown that the growth of the Si buffer layers evolved towards truncated pyramids whose top area can be controlled via the Si growth time. The number of Ge dots in a window, as well as their position, depends not only on the window dimension but also on the height of the Si buffer layers. Finally, we present some preliminary results on the optical properties of these Ge dots obtained from photoluminescence (PL) and Raman spectroscopies. [Copyright &y& Elsevier]