Si1 xGex Research Articles

High-Field Electron Transport in SiGe Alloy

Electron transport in unstrained Si1-x Gex (0≤x ≤0.4) alloy is studied in the present work using the Monte Carlo (MC) simulation technique. Electron transport characteristics (drift velocity, impact ionization (II) coefficient, etc.) are evaluated over a wide range of electric fields. It is found that not only low-field mobility but also saturation velocity and impact ionization coefficients are reduced with increasing Ge fraction due to alloy scattering. More importantly, the high-energy ( ε>2 eV) electron population is reduced to a much greater extent than the ionization coefficient. Simple analytical expressions for electron low-field mobility, saturation velocity and II coefficient which can be easily implemented in device simulation programs are proposed.

A fast X-ray method to determine Ge content and relaxation of partly relaxed Si1–xGex layers on silicon substrates

A fast X-ray method is presented to determine the Ge content and the relaxation of partly relaxed SiGe layers on Si substrates using a conventional powder diffractometer. The lattice parameters of the layer parallel and normal to the (001) substrate surface are obtained by a usual ω-2θ scan with symmetrical 004 reflection and an ω scan in asymmetrical reflection to measure the relative misorientation between inclined net planes of substrate and layer. The accuracy of this method is checked at a sample with pseudomorphic SiGe layer and its application is demonstrated at three partly relaxed samples with medium Ge content. Es wird eine röntgenographische Methode unter Verwendung eines konventionellen Pulverdiffraktometers vorgestellt, mit der eine schnelle Bestimmung des Ge-Gehalts und der Relaxation von teilweise relaxierten SiGe-Schichten auf Si-Substrat vorgenommen werden kann. Die Gitterparameter der Schicht parallel und senkrecht zur (001)-Substratoberfläche werden erhalten durch einen üblichen ω-2θ-Scan mit symmetrischer 004-Reflexion bzw. einem ω-Scan in asymmetrischer Reflexion, wodurch die relative Fehlorientierung zwischen den geneigten Netzebenen von Substrat und Schicht gemessen wird. Die Überprüfung der Genauigkeit der Methode erfolgt an einer Probe mit pseudomorpher SiGe-Schicht, und ihre Anwendung wird an drei teilweise relaxierten Proben mit mittlerem Ge-Gehalt demonstriert.

In-Situ Observation of Chemical Vapor Deposition of Thin Sige Films by Optical Reflection Interferometry

AbstractChemical Vapor Deposition of Si1-x Gex – films on Si (100) and of polycrystalline Si1-x Gex, layers on SiO2 – coated substrates have been performed at a pressure of 200 Pa in the temperature range of 500°C – 800°C, correspondingly. To observe the growth process and to characterize the growing thin films at deposition conditions an optical reflection interferometer (PYRITIERS) has been used. Comparing the data obtained at growth temperature with ex- situ measurements by spectroscopic ellipsometry the temperature dependence of optical constants of SiGe films have been evaluated. The reflectivity measurements during the deposition process allow to study the quality of the heteroepitaxial film, even in the initial stage of epitaxial growth.

Growth and Photoluminescence of Strained < 110 > Si/SilxGex/Si Quantum Wells Grown by Rapid Thermal Chemical Vapor Deposition

ABSTRACTWe report the first chemical vapor deposition growth and systematic photoluminescence study of strained Si1–xGex alloy layers on < 110 > Si substrates. Compared to < 100 > Si substrates, the same growth conditions yielded a slightly lower Ge composition, but a much lower growth rate. For thick layers, the relaxation along [110] direction is insufficient and lead to predominantly uniaxial strain in the the films. From the photoluminescence, the bandgap of strained Si1–x.Gex on < 110 > Si for 0.16 ≤ x ≤ 0.43 is determined and compared to theory. A strong “no-phonon” emission process in photoluminescence spectra of strained < 110 > Si/Si1–x.Gex/Si was observed as compared with that observed in < 100 > layers. Finally, quantum confinement shift of Si/Si0.71 Ge0.29/Si wells with a confinement energy up to 110 meV has been observed by varying the well width from 133 Å to 17 Å.

Extention of the “three partial rates” model to layer growth and composition of the ternary Si1–(x+y)GexBy system

AbstractThe previously published “three‐partial rates” model of Si1–xGex layer growth (Kühne 1992) has been extended for describing Si1–(x+y)GexBy ternary systems by taking additionally into account a partial rate of boron and a partial rate of boron‐originated silicon deposition. Silicon deposition from a silane‐germane‐diborane‐helium gas mixture at T = 500°C and Ptotal = 0.2 Torr is clearly enhanced by the presence of germane though to a low degree only, but not by diborane. Germanium partial rate as well as boron partial rate depends linearly on the partial pressure of the respective source gas. For illustration the data published by Murase have been used.

The Modeling Routes for the Chemical Vapor Deposition Process

AbstractThe purpose of this article is to present the modeling routes for the chemical vapor deposition process with a special emphasis to mass transport models with near local thermochemical equilibrium imposed in the gas-phase and at the deposition surface. The theoretical problems arising from the linking of the two selected approaches, thermodynamics and mass transport, are shown and a solution procedure is proposed. As an illustration, selected results of thermodynamic and mass transport analysis and of the coupled approach showed that, for the deposition of Si1-x Gex solid solution at 1300 K (system Si-Ge-Cl-H-Ar), the thermodynamic heterogeneous stability of the reactive gases and the thermal diffusion led to the germanium depletion of the deposit.

Safety-related systems. Competence, liability and practice : Alasdair Kemp. IEEE Review 350 (October 1992)

The chapter presents a discussion on epitaxial growth techniques and low-temperature epitaxy. The chapter focuses on the low-temperature epi growth of Si and Si1–xGex on silicon (Si), chemical vapor deposition (CVD) machines, growth mechanisms, surface treatment, and in situ doping growth of Si1–xGex/Si heterostructures. Because lowering the growth temperature generates more unexpected contaminations on the Si surface, it is very important to avoid any contamination on the Si surface during transport of the wafer into the reactor and during the wafer's stay in the reactor prior to deposition. To achieve high-quality epi growth of Si, it is essential to remove any contamination on the Si substrate by surface treatment before epi growth. In the molecular beam epitaxy (MBE) process, organic and metallic impurities on the Si surface were removed by wet cleaning, a thin protective oxide layer was formed to passivate the surface against recontamination during wafer transport into the reactor, and then the oxide layer was removed by thermal heating in an ultrahigh vacuum (UHV) environment.

Influence of growth conditions on the photoluminescence of pseudomorphic MBE grown Si 1-xGex quantum wells

The influence of growth conditions on the photoluminescence of SiGe quantum wells is presented. Growth temperatures above 600°C are found to be a prerequisite for a good layer quality. The variation of growth rates between 0.25 and 1 åA/s, however, has no significant effect on the spectra. With optimized growth conditions, strong excitonic dominated quantum well luminescence with line widths below 5 meV has been achieved.

A First Approach to CVD Si1–xGex Layer Growth by Means of Chemical Reaction Kinetics

AbstractA reaction mechanism will be suggested for interpreting Si1–xGex CVD layer deposition from a silicon source and germane reaction gas mixtures in order to explain the observed silicon layer growth increase in consequence of the presence of germane. A successive substitution of the hydrogen atoms available in germane molecules by silyl groups forming a silicon containing intermediate of germane will be assumed. It will further be supposed that both the original silicon source and the germane intermediates will independently be decomposed by chemical reactions leading to Si1–xGex CVD layer deposition from dichlorosilane‐germane‐hydrogen reaction gas mixtures at temperatures in the range of 600 ≦ T(°C) ≦ 900 as recently published by KAMINS and MEYER.

Strain Relaxation in Epitaxial Heterostructures: Sensitivity of High Resolution X-Ray Diffraction

ABSTRACTComparison of high resolution x-ray diffraction and transmission electron microscopy measurements of Si-based heterostructures demonstrates that diffraction is much more sensitive to strain relaxation than previously reported. This study used as-grown and annealed Si1-x Gex structures grown on (001) Si by UHV/CVD. (004), (113), and (115) rocking curves were employed. Using the TEM measurements as a quantitative guide, relaxation was observed in rocking curves when the misfit dislocation line density was as low as 1 μ-1. Also, interference fringes strongly depend on the presence of interfacial defects. At higher dislocation densities, the diffraction peak from the epitaxial layer broadens considerably but does not shift to a position that represents complete relaxation. Broadening of the substrate diffraction peak also occurs, which is due to dislocations that loop into the substrate.

Structural and analytical characterization of Si1-x Gex /Si heterostructures by Rutherford backscattering spectrometry and channeling, analytical electron microscopy and double crystal X-ray diffractometry

Structural and analytical characterization of Si1-x Gex /Si heterostructures by Rutherford backscattering spectrometry and channeling, analytical electron microscopy and double crystal X-ray diffractometry

Relaxed Si1−xGex Layers on Simox Avoiding a Lattice Mismatched Heterointerface

ABSTRACTFor the first time, Si1 xGex layers on amorphous SiO 2 were produced by modification of the Si surface layer of a SIMOX wafer. We used two alternative methods. An additional Si1.. Gey layer was deposited epitaxially on a SIMOX wafer followed by rapid thermal annealing. Diffusional intermixing of the layers produced a homogeneous Si1 xGex layer on SiO 2. In a second attempt, Ge was implanted into the Si surface layer and thermally treated. In both cases epitaxial Si1 xGex layers on SiO2 with minimum yield values around 9% were obtained. Rutherford backscattering and cross sectional transmission electron microscopy were used to characterize the new structures.

Sb Implantation in Si1–xGex/Si(100) Structures

ABSTRACTSolid phase epitaxial regrowth of Sb implanted strained Si1−x Gex alloy layers is reported. Two sets of Si1–xGex alloys with compositions of x=0.08 and x=0.18, MBE grown on (100)Si substrates, were implanted at room temperature with Sb− ions at energies of 200 and 100 keV, respectively, and a dose of 1015cm−2. These alloys were heat-treated in a rapid thermal annealing system at temperatures of 525, 550 and 575°C for durations between 5 and 600 sec. The study of the solid phase epitaxial regrowth was performed by Rutherford backscattering in the channeling mode. The measurements show a significant difference in the regrowth mechanism between the two alloys. For the Si0.92Ge0.00 alloy a fast regrowth process (faster than for Sb implanted Si or Si implanted SiGe layers) occured with an activation energy of 2.92±0.2eV. For the Si0.02Ge0.10 alloy the regrowth took place in two steps: a) a very fast initial process over a short distance, b) a regrowth process of the majority of the amorphous layer.

Raman and X-ray diffraction study of relaxation in Si–Si1–xGex strained-layer superlattices

We report a study of the relaxation of Si–Si1–xGex strained single layers and superlattices by Raman scattering spectroscopy, double crystal X-ray diffraction, and transmission and scanning electron microscopy. Samples of various dimensions and compositions were produced by molecular beam epitaxy at a growth temperature of 500 ± 30 °C. The thermal stability of the various specimens was investigated by annealing experiments at temperatures between 600 and 900 °C. Considerable deterioration of the crystal quality and progressive relaxation were observed in some of the samples. Relaxation occurred through formation of misfit dislocations at the first Si–Si1–xGex interface and these caused threading dislocations to form within the epilayer. The degradation of the superlattice interfaces on annealing is correlated with a sharp decrease in the acoustic mode Raman intensities. Strain values perpendicular to the growth direction as a function of annealing temperature are obtained from a kinematical simulation of the X-ray rocking curves. These results are compared with the frequency shifts of the longitudinal optical phonons in the Raman spectra. The results obtained for the critical layer thicknesses versus x are consistent with the excess stress model of Tsao and co-workers.