The mechanical properties of Si/Ge core-shell nanowires under a unixial tension are studied using molecular-dynamics simulation. The effects of anisotropy and the fraction of the core atoms on the Young's moduli of the core-shell nanowires are examined. The values of their Young's moduli deviate from those calculated using Vegard's law. Single atom chains are formed at the final stages of elongation of the nanowires.

We have performed molecular-dynamics simulations of heating, melting and recrystallization processes in amorphous silicon (a-Si) thin films deposited on glass during excimer laser annealing. By partially heating the a-Si surface region with 2 nm depth and removing thermal energy from the bottom of the glass substrate, a steady-state temperature profile was obtained in the a-Si layer with the thickness of 15 nm and only the surface region was melted. It was found that nucleation predominantly occurred in the a-Si region as judged by the coordination numbers and diffusion constants of atoms in the region. The results suggest that nucleation occurs in unmelted residual a-Si region during the laser irradiation and then crystal growth proceeds toward liquid Si region under the near-complete melting condition.

We have performed photoluminescence analysis of silicon rich oxide (SRO) and silicon rich oxynitride (SRON) samples deposited by plasma enhanced chemical vapor deposition (PECVD) and thermally annealed to cause the formation of silicon nanocrystals (Si-nc). Our purpose was to investigate the influence of nitrogen embedded into the oxide matrix on the photoluminescence properties of Si-nc. We found a large incorporation of silicon and a decrease of its diffusivity when the oxide is nitrogen rich. As a consequence the rate of crystallization for Si aggregates is slowed down when nitrogen is present in the oxide matrix.

The effects of high-pressure water vapor annealing (HWA) on the refractive index of PS have been studied. HWA was conducted at 260 °C and 1.3 MPa, for 3 h. The refractive index (real part n and imaginary part k) was estimated by fitting reflectivity spectra. HWA considerably modifies the layers refractive index. It enhances the optical transparency of PS, particularly at short wavelengths down to below 400 nm. Both n and k are significantly reduced by HWA between 400 nm and 850 nm. These results are attributed to the high level of oxidation of PS after HWA. The high transparency of the treated layers enables Si-based photonics in the full visible range and also in the near UV range. Distributed Bragg reflectors (DBRs) have been fabricated. The central wavelengths appear blue-shifted compared to untreated samples due to the reduced refractive index. Almost no changes could be found in the reflectivity properties after one year storage in air for HWA-treated DBRs. Therefore, HWA is very useful for getting stable practical photonics devices in the visible and near UV range.

Application of tensile strain to the Si(100) lattice is known to enhance carrier mobility in field effect transistors through modification of the Si band structure. Si is conventionally placed under tensile strain using methods such as Si3N4 capping for strained channel devices, and epitaxial growth of Si on a strain graded SiGe substrate for large area strain. The latter case preserves and propagates threading dislocations, and both cases require use of a bulk rigid substrate, which prohibits the use of strained Si in applications such as flexible electronics, or indeed in any application where strained Si is desirable on a non-epitaxial substrate. Elastically strained, single-crystal, Si-based nanomembranes, in which the release of a Si/SiGe/Si heterostructure from its growth substrate allows elastic strain sharing between the layers, circumvent these issues. These nanomembranes are extremely flexible, virtually dislocation-free, and transferable to almost any other surface.

We propose a novel form of graphene-like Si nanostructure based on ab initio total-energy calculation and geometry optimization, (MSi12)n, with M being transition metal atom. It has a three-layer structure, where the two layers of Si atoms in graphene-like positions sandwich another layer of transition metal atoms. The electronic structure may become semiconducting or metallic, depending on the choice of M and arrangement of Si atoms. This hypothetical material can be regarded as a Si-rich phase of transition metal silicide. A potential impact of our finding in forthcoming ultra-scaled Si technology is also discussed.

Nickel silicide is promising to be the choice material as contact to the source, drain, and gate for sub-65 nm and 45 nm CMOS devices. However, the thermal stability of NiSi is worse as the high resistivity phase of NiSi2 nucleates at about 750 °C and film agglomeration occurs even at a temperature as low as 600 °C. The process integration issues and formation thermally stable NiSi are needed to be understood and addressed. In order to obtain a thermally stable Ni-FUSI gate electrode, we introduced a novel integration process by using a two-step anneal process associating with properly tuned thickness of the initial Ni film and implant BF2 atoms during the poly-gate formation. As results, push the transformation of NiSi2 to a higher temperatures at about 900 °C. Several measurement techniques such as XRD, TEM, SEM and Resistivity are carried out to demonstrate its physical and electrical properties.

We recently reported the CVD growth of binary Ge1−ySny and ternary Ge1−ySixSny alloys directly on Si wafers using SnD4, Ge2H6 (di-germane), SiH3GeH3, and (GeH3)2SiH2 sources. Ge1−ySny is an intriguing infrared material that undergoes an indirect-to-direct bandgap transition for y ≥ 0.09. In addition, we have found that Ge1−ySny layers have ideal properties as templates for the subsequent deposition of other semiconductors: (a) they are strain-relaxed and have low threading-defect densities (105 cm−2) even for films thinner than 1 μm; (b) their low growth temperatures between 250°C and 350°C are compatible with selective growth, and the films possess the necessary thermal stability for conventional semiconductor processing (up to 750°C depending on composition); (c) they exhibit tunable lattice constants between 5.65 Å and at least 5.8 Å, matching InGaAs and related III-V systems; (d) their surfaces are extremely flat; (e) they grow selectively on Si and not on SiO2; and (f) the film surface can be prepared by simple chemical cleaning for subsequent ex-situ epitaxy. The incorporation of Sn lowers the absorption edges of Ge. Therefore, Ge1−ySny is attractive for detector and photovoltaic applications that require band gaps lower than that of Ge. Spectroscopic ellipsometry and photoreflectance experiments show that the direct band gap is halved for as little as y = 0.15. Studies of a Ge0.98Sn0.02 sample yield an absorption coefficient of 3500 cm−1 at 1675 nm (0.74 eV). Thus infrared detectors based on Ge0.98Sn0.02 could easily cover the U-(1565 nm-1625 nm), L-(1565 nm-1625 nm), and C-(1530 nm-1565 nm) telecomm bands. Photoluminescence studies show bandgap emission on thin GeSn layers sandwiched between higher bandgap SiGeSn barriers. We have made advances in p and n doping of GeSn and present results on electrical characterizations. GeSn also has application in band-to-band laser heterodiodes. The ternary system Ge1−x−ySixSny grows on Ge1−ySny-buffered Si. It represents the first practical group-IV ternary alloy, since C can only be incorporated in minute amounts to the Ge-Si network. The most significant feature of Ge1−x−ySixSny is the possibility of independent adjustment of lattice constant and band gap. For the same value of the lattice constant one can obtain band gaps differing by more than 0.2 eV, even if the Sn-concentration is limited to the range y < 0.2. This property can be used to develop a variety of novel devices, from multicolor detectors to multiple junction photovoltaic cells. A linear interpolation of band gaps lattice constants between Si, Ge and α-Sn shows that it is possible to obtain SiGeSn with a band gap and a lattice constant larger than that of Ge. We shall use this feature to make a tensile-strained Ge-on-SiGeSn telecomm detector with improved performance. The tensile-strain-induced direct gap of Ge can be used also for laser diodes and electroptical modulators.

The contribution of oxide-related emission in Photoluminescence (PL) spectra from Ge and Si nanocrystals mixture embedded in silicon oxide (Ge/Si-SiO2) and Si nanocrystals embedded in silicon oxide (Si-SiO2) thin film prepared by RF-magnetron co-sputtering method is investigated. All as-deposited thin films were annealed for 1 hour in the temperature range from 300 to 1100 °C in an Ar atmosphere. The samples were evaluated by using PL, Energy dispersive spectroscopy (EDX), Raman scattering and X-ray photoelectron spectroscopy (XPS) measurements. All the measurements were performed at room temperature. The maximum PL intensity of Ge+Si-SiO2 mixture thin film has increased more than the Si-SiO2 thin film by approximately 10 times. From the results of Raman scattering and XPS measurements, it is consider that the oxygen defect centers in the host material SiO2 increased by the diffusion of Ge. An increase in the PL intensity of Ge+Si-SiO2 mixture thin film is systematically discussed.

We first present an analysis of the band line-up in the case of SiGe/Si quantum wells and in the case of SiGe/Si self-assembled islands. The conduction and valence band diagrams are obtained from a 30 band k.p Hamiltonian which allows to describe simultaneously conduction and valence band states. The strain field is obtained from a microscopic valence force field theory. The band edge alignment is strongly dependent on the input parameters for this heterosystem. We determine the average valence band offset from photoluminescence measurements of heterostructures grown on relaxed SiGe buffer layers. A type II band line-up is calculated for all Ge compositions in the case of two-dimensional quantum wells and SiGe/Si self-assembled islands. The 30-band formalism allows the determination of the near-infrared interband recombination energy as a function of the self-assembled island structural parameters. We then present recent results obtained by embedding SiGe/Si self-assembled islands in two-dimensional photonic crystals. The photoluminescence of GeSi islands acts as an internal probe to characterize the optical properties of silicon-based two-dimensional photonic crystals designed for the near-infrared spectral range. Cavities, defect-free photonic crystals operated at the second Bragg order and two-dimensional photonic crystals fabricated on top of one-dimensional Bragg mirrors (2D + 1D) are described. We show that, in the case of 2D +1D structures, we can control the quality factor of optical modes at the second Bragg order by matching the resonance conditions and controlling the thickness of the layers. Photonic crystals with pure Ge layers are finally described.

This paper discusses the prospects of silicon as a Mid-wave Infra-red Raman crystal. As a specific example of novel devices that can be realized, we introduce the concept of multi-mode silicon Raman amplifiers and their application in infrared image pre-amplification. The same technology also has application in incoherent beam combining.

We have epitaxially grown Si/β-FeSi2/Si (SFS) structures with β-FeSi2 particles or β-FeSi2 continuous films on Si substrates by molecular beam epitaxy (MBE), and observed 1.6 μm electroluminescence (EL) at room temperature (RT). The EL intensity increases with increasing the number of β-FeSi2 layers. The origin of the luminescence was discussed using time-resolved photoluminescence (PL) measurements. It was found that the luminescence originated from two sources, one with a short decay time (τ∼10 ns) and the other with a long decay time (τ∼100 ns). The short decay time was due to carrier recombination in β-FeSi2, whereas the long decay time was due probably to a defect-related D1 line in Si.

A systematic study of nonlinear optical properties of silicon nanocrystals (Si-nc) grown by plasma enhanced chemical vapor deposition (PECVD) is reported. Nonlinear optical refraction and absorption have been measured by z-scan technique at three different time regimes and at different wavelengths to investigate both the thermal and electronic responses. For this purpose three different laser sources have been used. Different behaviors, as expected from the theory, for different pump pulse durations are observed.

The time resolved and DC photoconduction characteristics of Si nanowire devices are described. Si nanowires with diameters ranging from 20-100 nm were grown using the vapor-liquid-solid (VLS) growth mechanism under standard conditions and devices were fabricated in a back-gate field effect transistor (FET) configuration using simple photolithography. It is shown that under certain biasing conditions, illumination with light from light emitting diodes with wavelengths ranging from 480 nm to 625 nm causes changes in current as high as 4%. On the other hand, illumination by a broadband incandescent source causes a ∼4.1% percent change in current. Photoconductive decay curves show bi- and tri-exponential behavior, indicative of multiple potential recombination mechanisms occurring within the Si nanowire devices. p-n doped Si nanowires show similar behavior. Studies under various drain and gate voltages provides insight into the proposed mechanism. It is argued that the Shottky barrier plays a strong role in the observed photoconduction process in these wires, as do transitions involving surface and deep level trap states.

Materials processing with a gas cluster ion beam (GCIB) is an emerging technology that has been shown to produce novel material properties in the very near-surface (<40nm) regime. We have termed the process of doping with GCIB, infusion. Its principal characteristic enables room temperature shallow processing with high concentration gradients and no sharp interfaces. Results are presented from an investigation of GCIB GeH4 infusion into Si(100) substrates for the purpose of producing a strained Si(1-x)Ge(x) layer relative to the Si substrate. The as-infused samples exhibit surface Ge concentrations up to 100%, with a steep concentration gradient over ∼40 nm. Specifically, a broad series of post-processing tube-furnace anneals was investigated over a temperature range of 400 °C to 1200 °C and the samples were analyzed by channeling/RBS to look at quality of recrystallization and for evidence of strain in the lattice. Some anneal schedules included a VLTA (very low temperature anneal) first step followed by subsequent HTA (high temperature anneal). Evidence is shown for improved results with no Ge loss using two-step anneals. Channeling analysis was performed along the <100> and <110> directions relative to the Si(100) substrate. Measurements of the min for both the Ge and Si were made to assess crystal quality and to determine the degree of epitaxial alignment with the Si lattice. High-resolution axial scans along <110> were performed on selected samples to look for strain relative to the Si lattice. SIMS analysis of higher temperature anneals showed significant diffusion of Ge. Some samples were also examined by cross-sectional TEM. The best infusion samples show crystal quality comparable to a commercially available epi-grown Si75Ge25 control sample.

Silicon Photonics is experiencing a dramatic increase in interest due to emerging application areas and several high profile successes in device and technology development. For both performance and cost reasons, there is a worldwide trend towards miniaturising silicon photonic waveguides. The shrinking of the device dimensions provides advantages in terms of cost and packing density, modulation bandwidth, improved performance in resonant structures, and an increase in optical power density within the devices. However, the size reduction comes at some costs in increased difficulty in maintaining single mode operation of the waveguides whilst controlling the polarisation properties of the device.

For some applications, it is essential that optical modulators and filters, as well as other components, operate in the single mode regime. It is also desirable that these components are polarisation insensitive. Design of the waveguide, which is the basic element of these devices, is therefore crucial. Due to the compatibility with single mode fibre dimensions as well as the possibility of control of polarisation, rib waveguides represent promising candidates for integration in SOI. The main limitation for rib waveguides is that the bend radius cannot always be sufficiently small to minimise the device footprint. Strip waveguides, on the other hand, are often considered as a good choice in this respect, as they allow very small bend radii resulting in a compact footprint. However, polarisation dependence of these waveguides can be significant. Therefore, both waveguide configurations are investigated in this paper, together with the implications for optical modulators.

Following from this discussion, we also consider optical modulators that operate in the depletion mode with the intrinsic bandwidth of several tens of gigahertz. We have previously reported a modulator based on a small rib waveguide with the height of < 500nm for high speed operation. However, in this paper we consider slightly larger designs to accommodate polarisation independence. Finally we discuss the characteristics of ring and racetrack resonators based on both rib and strip waveguides and methods of improving free spectral range whilst considering polarization effects. Both theoretical and experimental results are presented. The maximum free spectral range that we have demonstrated experimentally is ∼43nm.

In this paper we discuss the role of local fields in the optical properties of silicon nanocrystals. Using a semiempirical tight binding approach, local field effects are included into the linear response theory, going beyond the standard independent particle approximation. The results show that local field effects give an important contribution to the optical properties of silicon nanocrystals, leading to a strong suppression of the absorption in the visible spectral range. This effect is attributed to the classical surface polarization contribution. A comparison between the atomistic tight binding approach and a classical dielectric model shows that the dielectric model gives reasonable results not only for large, but even for small silicon nanocrystals.

We present our work on the spin relaxation of electrons confined in SiGe islands. Ge islands are grown on unstructured and structured Si(100) substrates by MBE, and lead to strain in the Si layer that is deposited on top. These quantum dot structures are investigated by photoluminescence and electron spin resonance (ESR) experiments, the latter both in continuous wave and pulsed mode. We observe a g-factor and an ESR line width that correspond to Si conduction band electrons with additional inhomogeneous broadening.

We have synthesized the alkyl-passivated Si nanoparticles by a solution route, and have carried out the various spectroscopic studies in order to investigate their intrinsic optical properties, electronic structures, and surface chemistry. Photoluminescence (PL) spectra of the n-butyl-passivated Si nanoparticles with mean diameter less than 2 nm exhibit the strong ultraviolet-blue emission. Moreover, it is found that their valence-band maximum energies directly estimated from the synchrotron-radiation valence-band photoemission spectra correspond to the resonance features in the PL excitation spectra. Therefore, it is concluded that the PL from the present n-butyl-passivated Si nanoparticles originates from the electron-hole pair recombination between the modified valence-band and conduction-band due to the quantum size effect. From the synchrotron-radiation Si 2p core-level photoemission spectra, their interfacial electronic structures of these Si nanoparticles have also been characterized. From these results, we discuss the detailed electronic and chemical properties of alkyl-passivated Si nanoparticles.

We examine the nanostructural properties of Si/Si1−xGex island superlattices with 0.37 < x < 0.56 grown at 620-640 °C by molecular beam epitaxy. Analytical transmission electron microscopy (TEM) shows that during growth Ge atoms migrate towards the center of the large islands to maintain epitaxial growth and that the most regular structures are obtained at higher Ge composition when the built-in strain is also higher. High-resolution x-ray reciprocal space mapping shows that these heterostructures remain pseudomorphic and that the undulations are aligned along [010] directions and exhibit a long-range coherence and vertical correlation as revealed by the presence of strong satellites in a wave vector direction parallel to the surface. Raman spectra of these samples exhibit the usual Ge-Ge, Si-Ge and Si-Si vibrational modes. When compared with planar Si/Si1−xGex superlattices the Ge-Ge and Si-Ge Raman peaks are shifted to lower frequencies indicating an average alloy composition that is approximately x = 0.1 less than the nominal values, which is in general agreement with analytical TEM.