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A method of growing high-quality epitaxial Ge layers on a Si(100) substrate is reported. In this method, a 0.8 mm Si 0:1 Ge 0:9 layer was first grown. Due to the large lattice mismatch between this layer and the Si substrate, many dislocations form near the interface and in the lower part of the Si 0:1 Ge 0:9 layer. A 0.8 mm Si 0:05 Ge 0:95 layer and a 1.0 mm top Ge layer were subsequently grown on the Si 0:1 Ge 0:9 layer. The formed interfaces of Si 0:05 Ge 0:95 /Si 0:1 Ge 0:9 and Ge/Si 0:05 Ge 0:95 can bend and terminate the upward-propagated dislocations very effectively. The in situ annealing process was also performed for each individual layer. Experimental results show that the dislocation density in the top Ge layer can be greatly reduced, and the surface is very smooth, while the total thickness of the structure is only 2.6 mm.

We demonstrate the effect of the pre-growth heat treatment process on the nucleation properties of Ge dots grown on pit-patterned Si(001) substrates. The prefabricated 200 nm diameter pits inherently evolve into truncated inverted pyramids (TIPs) with (110) base edges and a 7°-9° sidewall slope during heat treatment; this morphology transformation is robust against variations in shape and orientation of the pit patterns. Uniform Ge dots with an areal density of 4 × 10(9) cm(-2) were obtained on the Si substrates having TIPs. Each TIP contains four aligned Ge dots locating symmetrically with respect to (110). These dots exhibit an elliptical dome shape with major axis oriented along (100). The nucleation position, shape and spatial orientation of these Ge dots coincide with the calculated surface chemical potential distribution of the TIP.

We have evaluated the thermal conductivity of Si/SiGe superlattice films by theoretical analysis and experiment. In experiments, the ultrahigh vacuum chemical vapor deposition is employed to form the Si/ Si 0.71 Ge 0.29 and Si/ Si 0.8 Ge 0.2 superlattice films. The cross-plane thermal conductivities of these superlattice films are measured based on the 3 method. In the theoretical analysis, the phonon transport in Si/ Si 1−x Ge x superlattice film is explored by solving the phonon Boltzmann transport equation. The dependence of the thermal conductivity of the Si/ Si 1−x Ge x superlattice films on the superlattice period, the ratio of layer thicknesses, and the interface roughness is of interest. The calculations show that when the layer thickness is on the order of one percentage of the mean free path or even thinner, the phonons encounter few intrinsic scatterings and consequently concentrate in the directions having high transmissivities. Nonlinear temperature distributions are observed near the interfaces, arising from the size confinement effect and resulting in a slight increase in the film thermal resistances. The interface resistance due to the interface scattering/ roughness, which is nearly independent of the film thickness, nonetheless dominates the effective thermal conductivity, especially when the superlattice period is small. Finally the experimental measurements agree with the theoretical predictions if the specular fraction associated with the interface is properly taken.

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