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We review the potential of low-energy plasma-enhanced chemical vapor deposition (LEPECVD) for the fabrication of strained Si and Ge heterostructures and devices. The technique is shown to be equally applicable to the formation of relaxed SiGe buffer layers, and to entire heterostructures including strained modulation doped channels. Pure Ge channels on Ge-rich linearly graded buffers are shown to exhibit low-temperature hole mobilities up to 120,000 cm2 V−1 s−1, limited by remote impurity and background impurity scattering rather than interface roughness scattering. Strained-Si modulation-doped field-effect transistors (n-MODFETs) with excellent frequency response have been fabricated by combining LEPECVD and MBE for buffer layer and active layer growth, respectively. Maximum oscillation frequencies of n-MODFETs above 140 GHz have been achieved for active layer stacks both on buffers linearly graded to a Ge fraction of 40% at a rate of 10% per micron, and on constant composition buffers which are 10 times thinner. The use of a thin buffer results in significantly less device self-heating. [Copyright &y& Elsevier]

We describe the construction and operation of an ultrahigh-vacuum system devoted to the study of thin film magnetism. The apparatus includes a growth chamber, where ultrathin films are deposited by molecular beam epitaxy, and a measurement chamber, where they are analyzed by a variety of electron spectroscopies. The electron spin can be controlled by using a fully characterized spin resolved electron gun and polarization analyzers. Test measurements on in situ grown Fe/MgO(001) samples are also presented as illustration of the system performances. [Copyright &y& Elsevier]

Abstract: We report on light modulation, detection, and emission characteristics of Ge/SiGe multiple quantum well waveguides using the same epitaxial growth and fabrication steps. As an electro-absorption modulator, the device exhibits the capability to achieve high extinction ratio with low swing bias voltages and high modulation bandwidth. As a photodetector, dark currents, optical responsivities, and high speed performance have been studied. High speed light detection up to 10Gb/s has been obtained simultaneously with good values of optical responsivity. As a light emitting diode, direct gap electroluminescence (EL) from the Ge/SiGe MQW waveguides has been experimentally demonstrated at room temperature within the spectral range of light modulation and detection. [Copyright &y& Elsevier]

Thermoelectric materials are one potential technology that could be used for energy harvesting. Here we report results from nanoscale Ge/SiGe heterostructure materials grown on Si substrates designed to enhance the thermoelectric performance over bulk materials at room temperature. The materials and devices are aimed at integrated energy harvesters for autonomous sensing applications. We report Seebeck coefficients up to 279.5±1.2 V/K at room temperature with electrical conductivities of 77,200S/m which produce a high power factor of 6.02±0.05mWm−1 K−2 and a ZT of 0.135±0.074 at room temperature. Methods for microfabricating modules will be described along with the first demonstration of power output from flip-chip bonded SiGe legs. [ABSTRACT FROM AUTHOR]

Abstract: A procedure for the quantitative measurement of composition and strain in epitaxial heterostructures by means of Raman spectroscopy for any Ge concentration is presented. The calibration of the parameters of this procedure involved the growth of a set of heteroepitaxial layers spanning the range from pure Si to pure Ge. Different strain conditions were established in a highly controlled way by tailoring the substrate lattice parameter. Through the comparative analysis of reciprocal space mapping and Raman spectroscopy we obtained a set of parameters for the phonon energy variation due to biaxial deformation, as well as calibration curves for the dependence of the Raman band frequencies on alloy composition. With these new calibrations, Raman spectroscopy provides an accuracy in the determination of composition and strain comparable to that of X-ray diffraction, but with the added advantage of high-spatial resolution and resonance-induced surface confinement. [Copyright &y& Elsevier]

Abstract: We compare four different selective etching solutions commonly used to highlight threading dislocations (TD), in SiGe hetero-epitaxial layers. The aim is to identify, amongst the many reported in the literature, an etching solution effective over the whole Ge concentration range. Etching experiments have been performed on Si1− x Ge x linearly graded relaxed buffer layers with a final germanium concentration x varying from to 0.9. All samples have been deposited on Si(100) by low-energy plasma-enhanced chemical vapour deposition (LEPECVD). The experimental results show that a variant of the so-called Schimmel-etch is successful in revealing TD over the Ge concentration range investigated. [Copyright &y& Elsevier]

Abstract: We present a comparison of two different techniques for the evaluation of Threading Dislocation Density (TDD) in Si1− x Ge x graded buffers: chemical etching and Electron-Beam-Induced-Current (EBIC) imaging. The samples analyzed consist of a series of linearly graded Si1− x Ge x buffers terminated by a constant composition layer with Ge concentration varying between 0.2 and 0.9. The films were deposited on Si(100) wafers by means of Low Energy Plasma Enhanced CVD (LE-PECVD). Our results indicates that EBIC proves to be a versatile method, which provides reliable information on the defect concentration up to a Ge concentration of . For higher values of x the information is approximated but yet reliable for the purpose of optimising the growth process. In order to perform EBIC measurements on samples with higher Ge concentrations , the Schottky diode fabrication has to be improved. [Copyright &y& Elsevier]

Abstract: A theoretical approach to the lattice dynamics of alloys within a valence force field framework is discussed. A modified Keating model, the anharmonic Keating, was employed to perform supercell calculations in order to investigate accurately the three Raman active optical phonon modes. Theoretical results on both relaxed and strained SiGe samples are shown. A detailed study of the biaxial strain-induced shift of phonon modes of epitaxial SiGe alloys has been performed in all the composition range. Furthermore, a comparison of experimental data with the model results on phonon strain shift coefficients will be also discussed. [Copyright &y& Elsevier]

This paper reviews the RF and noise performance of strained Si heterostructure field-effect transistors. For SiGe n-HFETs the high RF figures of merit fT=90 GHz, fMAX=188 GHz and noise performance NFMIN=0.3 dB at 2.5 GHz demonstrate the capabilities of these devices for microwave circuit applications. Recently some IC demonstrators have been successfully implemented. Strained Si HFETs fabricated on thick SiGe virtual substrates have been traditionally employed as a vehicle of study. Nevertheless these thick relaxed buffers involve some decisive disadvantages: Reduction of the wafer throughput, non-acceptable surface topology if implemented in mixed technologies like CMOS, and, in particular, self-heating due to low thermal conductivity of SiGe alloys compared to Si. In order to overcome these drawbacks several approaches to reduce the buffer thickness have been very recently developed. In this paper the RF and low frequency noise performance of SiGe HFETs prepared on very thin virtual substrates are reported. The potentialities of these technologies have not yet reached their limits. One can expect a great improvement by combining a proper device shrinking with very thin virtual substrates. These heterosystems could become the backbone of strained silicon devices towards microwave applications. [Copyright &y& Elsevier]