Rate-limiting step, as well as self-limited oxidation of SiGe alloys is so far under controversy. Contrasting to the monoparabolic growth mode for oxidation of Si, a parabolic growth mode and self-limited oxidation of SiGe alloys at different temperature are clearly observed depending on the oxidation time. With modified Deal-Grove model, we extract the parabolic rate constants related to the oxygen diffusion at different temperature and the activation energy of oxygen diffusivity finding that oxygen diffusion is still the rate-limiting step. We attribute this oxidation behavior to the strain effects associated with the volume change in converting Si/SiGe to SiO2/mixed oxide at different oxidation stages.

We report a room temperature study of the direct band gap photoluminescence of tensile-strained Ge/Si0.13 Ge 0.87 multiple quantum wells grown on Si-based germanium virtual substrates by ultrahigh vacuum chemical vapor deposition. Blueshifts of the luminescence peak energy from the Ge quantum wells in comparison with the Ge virtual substrate are in good agreement with the theoretical prediction when we attribute the luminescence from the quantum well to the c1-HH1 direct band transition. The reduction in direct band gap in the tensile strained Ge epilayer and the quantum confinement effect in the Ge/Si0.13 Ge 0.87 quantum wells are directly demonstrated by room temperature photoluminescence.

The strain relaxation in SiGe layer on silicon substrate during wet oxidation at 1000℃ was investigated. It was proposed that the competition between Ge accumulation and diffusion led to different strainrelaxation behaviors. At the very beginning, Ge atoms at the oxidizing interface were quickly accumulated due to the high oxidation rate resulting in the additional nucleation of misfit dislocations (therefore a lot of threading dislocations) to relieve stress after the thickness of the Ge condensed layer was larger than the critical value. And then, when the Ge accumulation rate was less than the diffusion rate, Ge content started to decrease from a maximum value and the strain in the SiGe layer was mainly relieved through surface roughing and the degree of strain relaxation reached a maximum. When the samples were further oxidized, Ge accumulation could be neglected because of the self-limiting oxidation and the Ge diffusion dominated the consequent processes. As a result, Ge content at the interface was reduced, with the contribution of the strain relaxation in SiO2 viscously, leading to the decrease of degree of strain relaxation in the SiGe layers slowly.

fully strin-relxed Si0.72 Ge 0.28 thin film w s grown on Si (100) substr te with combin tion of thin low-temper ture (LT) Ge nd LT-Si0.72 Ge 0.28 bufferfl yers by ultr high vcuum chemiclv pordeposition. The strin relxtion rtio in the Si0.72 Ge 0.28 film w s enh nced up to 99% with the ssist nce of three-dimensionl Ge isl nds and point defects introduced in the l yers, which furthermore fcilitted anultr-low thre ding disloc tion density of 5104cm 2 for the top SiGe film. More interestingly, no cross-h tch p ttern w s observed on the SiGe surf ce and the surfrce root-me n-squ re roughness was less thin 2nm. The temper ture for the growth of LT-Gel yer was optimized to be 3008℃.

The morphological evolution of SiGe films was investigated during vacuum thermal annealing. We found that Ge islands preferentially form in the process of decomposition of native oxide covering the SiGe layer, while pits form as an effective means of relaxing strain in the SiGe layer passivated with hydrogen during vacuum thermal annealing. The formation of small size Ge islands weakly depends on the strain relaxation of the SiGe layer. The size of Ge islands increases with Ge content in the initial SiGe layer and the maximum density of Ge islands is obtained for the SiGe layer with a lower Ge content of 0.06 among the investigated samples. A mechanism to form Ge islands on SiGe films rather than strain driven is proposed in terms of surface potential energy profile induced by the process of decomposition of native oxide.

SiGe heterojunction bipolar phototransistors based on Si1 yGey virtual substrate have been proposed in this paper. The current gain and external quantum efficiency of the heterojunction bipolar phototransistors are calculated by solving one-dimensional diffusion equations. The computed results show that external quantum efficiency increases with the increase of Ge content of Si1 yGey virtual substrate and a high external quantum efficiency of 142 can be obtained in the heterojunction bipolar phototransistor with ten periods of Ge/Si0.4Ge0.6 multi-quantum wells on virtual substrate with Ge content of 0.6. The dependences of external quantum efficiency and current gain on structure parameters of the heterojunction bipolar phototransistors are investigated in detail. It is useful for design and optimization of the heterojunction bipolar phototransistors.

Thermal annealing effects on a thin compositionally graded SiGe buffer layer on silicon substrate fabricated by oxidizing a strained SiGe layer are investigated with X-ray diffraction, ultraviolet Raman spectra and atomic force microscopy. Interestingly, we found that the surface roughness and the threading dislocation densities are kept low during the whole annealing processes, while the Ge concentration at the oxidizing interface decreases exponentially with annealing time and the strain in the layer is only relaxed about 66% even at 10008℃ for 180min. We realized that the strain relaxation of such a compositionally graded SiGe buffer layer is dominated by Si-Ge intermixing, rather than generation and propagation of misfit dislocations or surface undulation.

High-quality Ge epilayer on Si (100) substrate with an inserted low-temperature Ge seed layer and a thin Si0.77Ge0.23 layer was grown by ultrahigh vacuum chemical vapor deposition. The epitaxial Ge layer with surface root-mean-square roughness of 0.7nm and threading dislocation density of 5105 cm 2 was obtained. The influence of low temperature Ge seed layer on the quality of Ge epilayer was investigated. We demonstrated that the relatively higher temperature (3501℃) for the growth of Ge seed layer significantly improved the crystal quality and the Hall hole mobility of the Ge epilayer.

Optical and electrical properties of b-FeSi2 particles embedded in silicon matrix were improved by growing an un-doped silicon buffer layer at high temperature. With silicon buffer layer, the formation defects were prevented in the silicon matrix during the growth of b-FeSi2 and the subsequent annealing, which results in the narrow photoluminescence spectra. The diodes with silicon buffer layer showed smaller leakage current than those samples without silicon buffer layer. The thermal quenching of electroluminescence from such samples with silicon buffer layer occurred at higher temperature and the intrinsic band gap energy shift between silicon and b-FeSi2 was measured at about 0.23 eV.

Electroluminescence (EL) properties of Si-based light emitting diodes with b-FeSi2 particles active region grown by reactive deposition epitaxy are investigated. EL intensity of b-FeSi2 particles versus excitation current densities has different behaviors at 8, 77K and room temperature, respectively. The EL peak energy shifted from 0.81 to 0.83 eV at 77K with the increase of current density from 1 to 70 A/cm2. Temperature dependence of the peak energy can be well fitted by semi-empirical Varshni's law with the parameters of a ¼ 4.34e-4eV/K and b ¼ 110 K. These results indicate that the EL emission originates from the band-to-band transition with the band gap energy of 0.824 eV at 0K.