We have fabricated a series of a-SiNx/nc-Si/a-SiNx double-barrier structural samples by plasma-enhanced chemical vapor deposition (PECVD) and subsequent thermal annealing technique. The micro-structural properties of the samples were studied by using Raman scattering spectroscopy, planar and cross-section transmission electron microscopy (TEM). The electrical properties of the samples were investigated by frequency dependence of capacitance voltage (C-V) measurements. Charging effect in the nc-Si was exhibited through the hysteresis phenomena of the C-V curve and explained by F-N tunneling. For the thicker SiNx barrier layer samples, Coulomb blockade effect was observed in C-V curve for the sample with thinner SiNx barrier layer, in which two capacitance peaks appeared, and explained by direct tunneling of electrons into the nc-Si through the tunneling SiNx layers. From the interval between the two peaks, the Coulomb charging energy of nc-Si dot was estimated.

Optical activation of Si nanowires (Si-NWs) using sol-gel derived Er-doped silica is investigated. Si-NWs of about 100 nm diameter were grown on Si substrates by the vapor-liquid-solid method using Au catalysts and H2 diluted SiCl4. Afterwards, Er-doped silica sol-gel solution was spin-coated, and annealed at 950 °C in flowing N2/O2 environment. Such Er-doped silica/Si-NWs nanocomposite is found to combine the advantages of crystalline Si and silica to simultaneously achieve both high carrier-mediated excitation efficiency and high Er3+ luminescence efficiency while at the same time providing high areal density of Er3+ and easy current injection, indicating the possibility of developing sol-gel activated Si-NWs as a new material platform for Si-based photonics.

Uniform arrays of nanopillars, nanospikes, nanorings and rings atop nanopillars were fabricated using modified nanosphere lithography on the Si(111) surface and observed using AFM and SEM. A self-assembled monolayer mask which utilized 450±10nm polystyrene spheres were used as an etch mask during a fabrication process of physical Ar+ ion bombardment followed by SF6 RIE to produce nanopillars with flat tops that could be as large as 210nm in height and 175nm in diameter. Nanospikes of approximately the same height were fabricated made with a FWHM of 250nm. The initial Ar+ ion bombardment step was varied to achieve up to 4 times faster etch rates and narrowed widths in the nanospikes. Both types nanostructures systems were “self-wired” which is an intrinsic result of this fabrication process. Self-wired nanorings and rings atop nanopillar structures were also fabricated using a two step etching process along with sonication. The nanorings had inner and outer diameters of 225±5nm and 175±5 nm, respectively and were up to 20nm in height and their nanowire connectivity could be made optional by a judicious choice of solvent for sonication. The self-wired Si nanostructures were also “dressed” with self-assembled Ge quantum dots. These Ge/Si nano-architectured structures possess the basic framework for fabricating novel nanoelectronic and nano-optoelectronic devices in the foreseeable future.

SiC nanowire was grown by APCVD using single precursors. Grown SiC nanowires had 10∼60nm diameters and lengths of several micrometers. Nanowire's diameters and lengths were varied with kind of catalysts. Nanowire's growth scheme was divided by two regions with diameter of nanowire. At first region, nanowire was grown by VLS (vapor-liquid-solid) mechanism, but at the second region, nanowire growth was made by VS (vapor-solid) reaction. These differences were made from limitations of growth rate and deactivation effects. Growth temperature, time and flow rates of source gases were affected nanowire's diametesr and its lengths. And kind of catalysts, coating methods and precursors were affected growth direction and microstructures too.

Samples of Ge Nanowires (Ge NWs) grown by chemical vapor deposition (CVD) on single crystal, (100) and (111) oriented Si substrates were studied with respect to their electrical properties. Using different contact geometries, direct current (DC) and alternating current (AC) electrical and photoelectrical measurements were carried out at room temperature. A rectifying junction behavior was observed indicating a low defect density at NWs/substrate heterointerface. AC conductance exhibits significant frequency dependence with a power law behavior, suggesting that carrier transport in Ge NW volume is associated with hopping processes.

While electroluminescence has been demonstrated at terahertz frequencies from Si/SiGe quantum cascade emitters, to date no laser has been achieved due to poor vertical confinement of the optical mode. A method of increasing the vertical confinement of the optical mode for a Si/SiGe quantum cascade laser is demonstrated using silicon-on-silicide technology. Such technology is used with epitaxial growth to demonstrate a strain-symmetrised 600 period Si/SiGe quantum cascade interwell emission and the polarisation is used to demonstrate the optical confinement. Electroluminescence is demonstrated at ∼3 THz (∼100 μm) from an interwell quantum cascade emitter structure. Calculated model overlap and waveguide losses for ridge waveguides are comparable to values from GaAs quantum cascade lasers demonstrated at terahertz frequencies. The effects of high doping levels in Si/SiGe quantum cascade structures is also investigated with impurity emission demonstrated rather than intersubband emission for the highest doping levels used in the cascade active regions.

Effect of pre-deposited boron atoms on self-assembled growth of Ge islands on Si(100) substrate by UHV/CVD was investigated by atomic force microscopy (AFM). Proportion of dome-shaped Ge islands increases with the increasing of flux of B2H6. Quite uniform dome-shaped Ge quantum dots with size distribution of less than ±3%, which is narrower than the size distribution of typical bimodal self-assembled Ge dots, were obtained after appropriate boron pre-deposition. Based on the shape transition model we proposed before, the uniform size and shape distributions after boron pre-deposition were explained. The results show that boron pre-deposition can be used to fabricate uniform Ge quantum dots to meet the requirements of opto-electronic devices.

In this paper we report the fabrication and experimental characterization of photoluminescent coupled multiple microcavity 1-Dimensional photonic bandgap structures for specific photonic applications. These structures have been prepared on silicon substrate as well as free standing. The comparision with theory gave a good fit showing desired structure formation for more than 184 layered structure. These structures can be useful for a large variety of applications such as silicon lasers.

Silicon carbide nanowires were grown via a self-organized process. Some of the nanowires showed complex diameter fluctuations. The fluctuation was studied from the viewpoints of random walk and fractal. Power spectrum analysis of a fluctuation revealed that the fluctuation was not periodic and that the spectrum was colored. The distribution of increments had a fat tail which was not Gaussian but obeyed power law. Thus the diameter fluctuation was interpreted as a Lévy Flight. In addition, the fluctuation also showed multiaffine scaling.

Several methodologies are developed for large-scale atomistic simulations with fully quantum mechanical description of electron systems. The important methodological concepts are (i) generalized Wannier state and (ii) Krylov subspace. Test calculations are done with upto 106 atoms using a standard workstation. As a practical nanoscale calculation, the 10 nm scale structure in cleavage process of silicon is investigated. Discussions are focused mainly on the stable (experimentally observed) (111)-(2 × 1) cleavage process. Surface reconstruction and step formation are observed and compared with experiments. These processes are analyzed by the quantum mechanical freedoms of electron system, such as the local density of states (LDOS). We also observed the bending of cleavage plane into the (111) plane from other planes, which is a direct evidence of the stability of the (111) cleavage mode. Finally, several common aspects between cleavage and other phenomena are discussed from a general viewpoint of 10 nm scale structure.

We report about the formation of Si1-xGex nanocrystals (NC) in an oxide matrix after oxidizing a polycrystalline Si0.7Ge0.3 layer in wet and dry conditions. We have characterized the NC by Energy Filtered Transmission Electron Microscopy (EFTEM). EFTEM images analyses show the evolution of the oxidation of polycrystalline Si0.7Ge0.3 layer. We observe that a layer with Ge-rich nanoclusters is formed. For wet oxidations we find Ge-rich Si1-xGex nanocrystals while for dry oxidations Si is oxidized faster and Ge is completely segregated. Results are contrasted with infrared and Raman spectroscopies. In conclusion, wet oxidation seems to be preferable to oxidize polycrystalline Si1-xGex to obtain Ge-rich NC embedded in an oxide matrix, as both Ge and Si are oxidized, in contrast to dry oxidation, where Ge is mainly segregated.

Light-emitting silicon nanocrystals (nc-Si) have attracted much interest due to their importance for optoelectronic devices. Electron hole recombination in a quantum confined system is generally considered as the theoretical frame explaining the photoluminescence (PL) origin. However, there is still a living debate, in particular regarding the PL decay dynamics. The decay is not single exponential and decay curves described by a stretched exponential law were systematically reported for all types of nanocrystalline silicon. The origin of this multi-exponential decay is often attributed to migration effects of the excitons between nanocrystals. In contrast to these approaches, the absence of carrier hopping has been demonstrated experimentally in porous silicon. In order to elucidate this question, specific samples were prepared, consisting in deposits made from gas phase grown silicon nanocrystals with different particle density. The nanoparticles were synthesized by laser pyrolysis of silane in a gas flow reactor, extracted as a supersonic beam, size-selected, and deposited downstream as films of variable densities by changing the deposition time. The nanoparticle number densities were determined by atomic force microscopy. Time-resolved photoluminescence measurements on these films were carried out as a function of the film density and at different PL wavelengths. The reported results showed photoluminescence properties independent of the film density. Even in the very low density film (∼4*109 particles/cm2) where nanoparticles are completely isolated from each other, the decay kinetics corresponds to a multi-exponential law. This means that exciton migration alone cannot explain the stretched exponential decay. Its origin must be linked to an intrinsic characteristic of the nc-Si particle. In this paper, the experimental results are described in more details and compared to the theoretical predictions available in the frame of the quantum confinement model. Then, the possible origins of the multi-exponential character of the decay dynamics is discussed, and the particular properties of the PL in indirect band-gap semiconductors emphasized.

We have proposed an advanced method for formation of semiconductor thin films at substrates temperatures below 100K. We have synthesized amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) films using low-energy electron-beam-induced-chemical vapor deposition (EBICVD) onto cooled substrates which adsorb source gases (SiH4 or Si2H6) at cryogenic temperature. The temperature dependence on growth rate of the films, hydrogen content and optical constants were investigated. The μc-Si:H could be formed at 40–45 K on SiO2 using He-discharged-EBICVD with SiH4. The crystallinity of silicon was evaluated by Raman scattering spectroscopy and X-ray diffraction.

A new metal catalysis-free method of fabricating Si or SiO2 nanowires (NWs) compatible with Si CMOS technology was proposed by annealing SiOx (x<2) films deposited by plasma -enhanced chemical vapor deposition (PECVD). The effects of the Si content (x value) and thickness of SiOx films, the annealing process and flowing gas ambient on the NW growth were studied in detail. The results indicated that the SiOx film of a thickness below 300 nm with × value close to 1 was most favorable for NW growth upon annealing at 1000–1150°C in the flowing gas mixture of N2 and H2. NWs of 50–100nm in diameter and tens of micrometers in length were synthesized by this method. The formation mechanism was likely to be related to a new type of oxide assisted growth (OAG) mechanism, with Si nanoclusters in SiOx films after phase separation serving as the nuclei for the growth of NWs in SiOx films>200nm, and SiO molecules from thin SiOx film decomposition inducing the NW growth in films<100nm. An effective preliminary method to control NW growth direction was also demonstrated by etching trenches in SiOx films followed by annealing.

We have investigated direct current (DC) operating voltage and luminescence properties of electroluminescent (EL) devices with and/or without a silicon dioxide (SiO2) layer in nanocrystalline Si (nc-Si) region/Si substrate interface. The device with the SiO2 layer showed red luminescence with a peak at 670 nm by applying the DC operating voltage above 4.0 V. When the SiO2 layer in the device was completely removed by the hydrofluoric acid (HF) treatment, the red luminescence from the device was observed at the DC operating voltage of 2.0 V. Moreover, the luminescent intensity was also increased more than one order of magnitude, because carriers were efficiently and easily injected into the nc-Si region by the removal of SiO2 layer. The red luminescence from the device could be clearly seen with the naked eye under the DC operating voltage above 3.0 V. These results indicate that the removal of SiO2 layer leads to the lowering of DC operating voltage and increase of luminance for the nc-Si based EL device.

Size control of silicon nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) as catalysts were investigated. The diameter of SiNWs decreased with decreasing synthesis temperature and content of Ni catalyst. Gradual down shift and asymmetric broadening of Si optical phonon peak depending on the diameter of SiNWs were observed for continuously, thermally oxidized SiNWs and SiNWs with smaller diameters formed at lower temperature. This can be interpreted by the phonon confinement effect. On the other hand, further thermal oxidation produced an upshift of the optical phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the surface oxide layers formed around the SiNW cores, resulting in a downshift of the optical phonon peak.