Lam H. Nguyen

Kinetics of Ge growth at low temperature on Si(001) by ultrahigh vacuum chemical vapor deposition

The growth of germanium at low temperature by ultrahigh vacuum chemical vapor deposition on Si(001) is investigated in real time by reflection high-energy electron diffraction. These observations are complementarily checked by atomic force microscopy, Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray diffraction experiments. It can be seen that the currently observed Stranski–Krastanov-related two-dimensional (2D) to three-dimensional transition is avoided at 330°C and that the major part of the relaxation process occurs during the deposition of the first two monolayers. Then, the measured in-plane lattice parameter evolves slowly and approaches that of bulk Ge after deposition of 50 monolayers. The corresponding relaxation equals 83%. The resulting surface is flat, with a rms roughness of 0.55nm. The relaxation is found to be mainly due to misfits dislocations located at the Ge∕Si interface. Regrowth experiments at 600°C show that the low-temperature films are not stable...

Selective growth of Ge quantum dots on chemically prepared SiO2/Si(001) surfaces

Abstract We report, in this paper, on selective growth of Si buffer layers and of Ge quantum dots on thermally desorbed SiO 2 /Si surfaces. The oxide layers with a thickness of about 6–8 A were chemically grown by using the standard wet Radio Corporation of America (RCA) cleaning method. We show that both the oxide desorption process and the growth of Si buffer layers can be monitored by using in situ reflection high energy electron diffraction. The growth of Si buffer layers is showed to process via the formation of pyramidal islands formed by {113} facets. Those facets grow until the (001) top layer disappears and are showed to be an additional parameter to control the nucleation process of Ge dots. By monitoring the facet formation during Si growth, we show that it is possible to form one Ge dot per window.

Vertical ordering in multilayers of self-assembled Ge/Si(001) quantum dots

The effect of vertical ordering in multilayers of self-assembled Ge/Si(001) quantum dots was investigated by a combination of structural and optical characterizations via in situ reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and photoluminescence spectroscopy. We show that the vertical ordering observed in quantum-dot multilayers is characterized not only by the alignment of islands along the growth direction but also by a reduction of the critical thickness. The better the vertical ordering, the more pronounced the reduction of the critical thickness is observed. Such an evolution of the critical thickness could be explained by elastic strain fields induced by buried islands and propagate through the spacer layers. An important result issued from this work is the realization of multilayers in which dots have equal size in all layers. Furthermore, experiments performed on the transformation of the island shape suggest that preferential nucleation induced by surface roughness may be the main mechanism responsible for the vertical ordering in quantum-dot multilayers.The effect of vertical ordering in multilayers of self-assembled Ge/Si(001) quantum dots was investigated by a combination of structural and optical characterizations via in situ reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and photoluminescence spectroscopy. We show that the vertical ordering observed in quantum-dot multilayers is characterized not only by the alignment of islands along the growth direction but also by a reduction of the critical thickness. The better the vertical ordering, the more pronounced the reduction of the critical thickness is observed. Such an evolution of the critical thickness could be explained by elastic strain fields induced by buried islands and propagate through the spacer layers. An important result issued from this work is the realization of multilayers in which dots have equal size in all layers. Furthermore, experiments performed on the transformation of the island shape suggest that preferential nucleation i...