Zhang Xiang-Jiu

Extremely Narrow Sb Delta-Doped Epitaxial Layer Characterized by X-Ray Reflectivity

An Sb delta doping layer in silicon is grown at the temperature of 300°C by silicon molecular beam epitaxy and characterized by the small angle x-ray reflectivity measurement using synchrotron radiation beam. The oscillations of the reflectivity caused by dopant Sb at Q as large as 14.5 are detected. Simulation of this curve as a whole shows that the total amount of dopant Sb is 0.15 monolayer and is restricted to two atomic layers. An extremely narrow Sb delta doping structure without Sb segregation is thus obtained at the growth temperature of 300°C as verified by the experiment.

SiGe Optical Waveguide Modulators Based on the Plasma Dispersion Effect

Based on plasma dispersion of Si1-xGex, the single mode waveguide modulators consisting of Si1-xGex/Si and Si/Si1-xGex/Si which were grown by molecular beam epitaxy have been fabricated. For Si1-xGex/Si structure, the switch current and insertion loss at wavelength 1.3 μm are 36 mA and 2.8 dB, respectively. The switching response time is 40 ns.

Highly Strained Si Films with Ultra-low Dislocation Density Grown on Virtual Substrates of Thin Thickness

By using compositionally graded SiGe films as virtual substrates, tensile strained Si films with the strain of 1.5% and the threading dislocation density less than 1.0 × 105 cm−2 are successfully grown in micron size windows by molecular beam epitaxy (MBE). The thickness of the virtual substrates was only 330nm. On the surface of the s-Si films no cross-hatched lines resulting from misfit dislocations could be observed. We attribute these results to the edge-induced strain relaxation of the epitaxial films in windows, and the patterned virtual substrates with compositionally graded SiGe films.

MBE Growth of Highly Relaxed Si0.45 Ge0.55 Films with Very Low Misfit Dislocation Density on Si (001) Substrates

We investigate the molecular-beam-epitaxy growth of highly relaxed Si0.45Ge0.55 films with very low dislocation densities. By using the Si3N4 film as the mask material, the Si0.45Ge0.55 film can be grown on a compositionally stepwise graded SiGe buffer layer in 3 μm×3 μm windows on a Si (001) substrate. Raman scattering spectroscopy measurement shows that more than 90% strain of the Si0.45Ge0.55 film is relaxed, and almost neither misfit dislocation lines nor etch pits of thread dislocations could be observed when the sample is etched by the modified Schimmel etchant. We suggest that the results can be explained by influence of the edge-induced strain relaxation of the epitaxial film and the edge-induced stress of the mask material.

Si1-xGex/Si Single-Mode Rib Waveguides with 0.5 dB/cm by Molecular Beam Epitaxy

Si1-xGex/Si single-mode rib waveguides with 0.5 dB/cm losses have been fabricated, in which the SiGe layers are grown by molecular beam epitaxy. The single-mode waveguide dimensions determined experimentally are consistent with the single-mode theory of SiGe waveguides.

Ge BEAM TREATMENT OF Si SUBSTRATE FOR MOLECULAR BEAM EPITAXY

A new surface cleaning method for Si MBE is described in which a very weak Ge beam flux is deposited on the surface for removing the thin passivative layer of SiO2 on the Si substrate. It has proved that the SiO2 will react with Ge at a relatively low temperature (620° C), and as a result, the oxide layer becomes volatile. Here the high temperature annealing in the conventional Shiraki method is no longer required, and since the oxide layer is removed in ultra high vacuum, only very little carbon contamination may occur. Furthermore, to reduce the excessive Ge on the substrate surface, Ge is deposited at 620° C and then the sample is annealed at 700° C; the residual Ge atoms on Si substrate can be reduced to less than 0.1 monolayer (ML). Ge beam treatment turns out to be an effective low-temperature Si surface-cleaning method, especially for the heteroepitaxial growth of GexSi1-x/Si.