Nanocrystalline silicon films are prepared by plasma enhanced chemical vapour deposition of silane under the conditions of high hydrogen dilution (3:100). The film structure consists of nanoclusters 0.8 to 5 nm in size (volume fraction 30%) embedded in an amorphous matrix. The Taue gap of the amorphous matrix is 1.95 to 2.05 eV depending on deposition parameter. These films are characterized as regards photoluminescence (PL) and, prepared to p-i-n structures, electroluminescence (EL). The PL and EL agree in (i) luminescence peak at 1.9 eV, i.e. small Stokes shift, (ii) almost no temperature dependence between 77 K and 293 K, (iii) fast kinetics with time constant of a few 10−8 s. These data can be understood in terms of quantum confinement in Si nanocrystallites smaller than around 2 nm. The EL in addition exhibits a luminescence band extending up to 3 eV, which can be interpreted by interband transition due the hot carriers.

The objective of this work is to find a material to replace amorphous hydrogenated silicon used as photosensitive part in the “retina” of an “electronic eye”. For that reason, ZnS, ZnSe, CdS and CdSe were chosen for investigations. Thin films, prepared by chemical vapour deposition, were characterized by transmission electron microscopy. The observed microstructures were correlated with the optoelectronic properties of these materials. CdSe was found to be the most promising material for our application. Hence, the influence of a dielectric interlayer and the effects of additional annealing treatments were analyzed for CdSe and will be discussed with respect to the optimization of the material.

Experimental works have been reviewed on poly-Si/poly-SiCx hetero TFTs aiming at extremely low off-current even under intense light illumination conditions with reasonable field-effect mobility. The results indicated that the hetero TFT having the stacked poly-Si/poly-SiCx layers is promising as a switching device in matrices

We have utilized a recently developed transient two-dimensional model for simulating localized beam-induced melting and solidification of thin silicon films on SiO2. Specifically, by tailoring the lateral beam profile, we simulate those situations that are encountered in the artificially-controlled superlateral growth (ACSLG) method, in which various techniques are utilized to irradiate the sample in preselected regions of a silicon film. The spatially and temporally localized character of heating is simulated by introducing a time-dependent two-dimensional heat-source function. The evolution of melt-creation and ensuing solidification is studied as a function of incident energy density and film thickness. The results show two distinct types of behavior as a function of incident energy density: at low energy densities, partial melting and predominantly vertical solidification occur; while at high energy densities, complete melting of the irradiated portion of the film is followed by rapid lateral solidification.

Recognizing that the processing window in conventional excimer laser crystallization corresponds mainly to the partial melting regime, and that this can be properly simulated using a one-dimensional model, we investigate numerically the melting and solidification of thin silicon films on SiO2. Here a portion of the silicon film is melted and subsequent vertical solidification is initiated from the lower interface bounding the unmelted region. Upper and lower energy density limits for this regime are calculated for crystal silicon films of thickness 10 to 300 nm, and for pulse duration ranging from 10 to 200 ns. These calculations show that increasing pulse duration requires proportionally more incident energy density to partially melt the film, while decreasing film thickness reduces the range of energy densities over which partial melting can occur. The results are explained in terms of characteristic thermal diffusion distances and the enthalpy change associated with melting. In view of the results we discuss optimization of the conventional excimer laser crystallization and the avoidance of complete melting during the process.

This paper describes an extension of the sequential lateral solidification (SLS) method for producing single-crystal Si regions in predetermined locations on thin Si films on SiO2. This is accomplished by manipulating the shape of the solidification front in order to exploit the tendency of grain boundaries to propagate nearly perpendicular to the melt interface. Specifically, we employ a chevron-shaped beamlet to select and grow the grain at the chevron's apex for propagation, resulting in a well-defined single-crystal region. Many such chevrons are processed concurrently—each one leading to a single-crystal region at a precisely determined location, and each one being large enough for complete inclusion of an entire thin-film transistor (TFT) device. Microstructural examination of defect-etched SLS material using optical microscopy reveals unambiguously that single-crystal regions free of high-angle grain boundaries are produced.

Epitaxial Si(1-y)Cy substitutional alloy layers are prepared on monocrystalline silicon substrates by carbon multiple energy ion implantation followed by XeCl excimer laser annealing on large surfaces. Structural analysis of the films before and after laser annealing are made very precisely using spectroscopie ellipsometry (SE), x-ray diffraction (XRD) and Rutherford backscattering (RBS) techniques. We show that annealing energy densities higher than 2J/cm2 result in monocrystalline epitaxial layers with low quantity of defects. The lattice contraction due to the carbon inclusion increases with the implanted C concentration up to about 1.1%. For higher values a more complex behaviour is observed with partial (or total) relaxation of the layer and/or carbide formation‥

The a-Si/poly-Si thin film tandem solar cell is a promising candidate for low-cost solar cells. We have conducted R&D on poly-Si thin film using the Solid Phase Crystallization (SPC) method from amorphous silicon (a-Si). To improve the film quality of SPC poly-Si, we have developed a new SPC method called the partial doping method. This method features two stacked starting a-Si layers, a P-doped layer and a non-doped layer. Nucleation occurs in the P-doped layer, and the non-doped layer is the crystal growth layer. For the nucleation layer, we developed a Si film with a unique structure, which features relatively large crystallites (-1000A) embedded in a matrix of amorphous tissue. By combining these technologies, a conversion efficiency of 9.2% was obtained for poly-Si thin-film solar cells. For further improvement in the conversion efficiency, based on the concept of “independent control of nucleation and crystal growth”, it is necessary to combine the best fabrication methods for each layer. A high conversion efficiency of more than 12% was found possible by using the CVD method and a new back surface reflection structure.

Poly-silicon films have been prepared by hot-wire chemical vapor deposition (HWCVD) from hydrogen diluted silane gas at a low temperature (430 °C). The optical gap of the poly-silicon films is 1.1 eV, though with a higher optical absorption than c-Si. The grains have a preferential orientation (220) perpendicular to the substrate with an average crystallite size of 70 nm. The crystalline volume fraction is 95% with complete coalescence of grains. Large structures up to 0.5 μm could be observed in the AFM micrograph. The activation energy (0.54 eV) and the low carrier concentration (1011 cm−3) indicate a fully intrinsic nature of the films. The μτ product of carriers is 7.1×10−7 cm2V−1 whereas the ambipolar diffusion length (LD) is 334 nm. The excellent photo-conductive properties are attributed to the low (∼1017 cm−3) defect density. The HWCVD poly-silicon films showed a very small temperature dependence of mobility, indicating negligible trapping of carriers at the grain boundaries. Preliminary n-i-p cells incorporating poly-silicon i-layer yielded 3.15 % efficiency.

Polycrystalline silicon (poly-Si) films are deposited at temperatures lower than 300–400°C by the cat-CVD method. In the method, a SiH4 and H2 gas-mixture is decomposed by catalytic cracking reactions with a heated tungsten catalyzer placed near substrates. Carrier transport, optical and structural properties are investigated for this cat-CVD poly-Si. The films show both large carrier mobility and large optical absorption for particular deposition conditions. The cat-CVD poly-Si films are found to be one of the useful materials for thin film transistors and thin film solar cells.

A pulsed-gas intermittent deposition technique is used to deposit high crystallinity hydrogenated micro- or poly-crystalline silicon using silane and hydrogen. This method has been used to deposit crystallites that are comparable to those obtained using PECVD of fluorinated silanes. RHEED and TEM have been used to understand the nucleation process. The pulsed-gas method is promising for depositing polycrystalline silicon and subsequent use in thin film transistor applications.

Polycrystalline silicon thin films were grown on glass by two-steps, i.e., deposition of seeds on glass (1) and growth epitaxy-like on the seeds (2). For the growth of seeds, the surface reaction was intentionally enhanced by impingment of atomic hydrogen at rather high temperature (450 °C). Strongly textured polycrystalline Si exhibiting (220) preferential orientation was grown epitaxy-like on the seeds.

The composition variation and strutural properties of poly-SiGe thin films were investigated by Reactive Thermal CVD with Si2H6 and GeF4. Deposition of the films was carried out at a low temperature of 450°C on oxidized silicon substrates using different growth parameters, i.e., the source gas flow ratio (Si2H6/ GeF4) and thegas flow rate. The structural profiles of as-deposited films were characterized by X-ray diffraction (XRD) and Raman scattering spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

All these films show (220) preferential orientation. The mole fractions of Si in poly-SixGe1−x films were estimated to be from 0.95 to 0.05 for x by using Vegard's law for the XRD peaks. TEM observation revealed that high crystallinity was well established even in poly-Si0.95Ge0.05 films owing to the direct nucleation on the substrate surface.

Inexpensive full-wafer SOI substrates are appealing for various applications such as ULSI. As an attempt to achieve this goal, low-temperature deposition of silicon on novel porous Si-on-insulator (PSOI) substrates was performed in this work. The bottom insulator was obtained by anodically oxidizing a pre-formed porous silicon film in HCl solution. The thickness, uniformity and quality of the resulted bottom oxide layer as well as the residual porous silicon layer above were well-controlled. Low-temperature PECVD growth of silicon on the PSOI wafer was conducted by using the residual porous silicon as the seed. Cross-sectional TEM pictures and electron diffraction patterns showed that poly-Si films were formed on PSOI substrates under the conditions of 98% hydrogen dilution ratio, 20 Watts RF power, and 300°C substrate temperature. Further thermal annealing at 1050°C for 30 minutes significantly enhanced the crystallinity of the deposited films. Combined with the excellent insulation ability of the bottom oxide, the technique is suitable for future inexpensive full-wafer SOI fabrication.

Polycrystalline silicon (polySi) is widely used in the semiconductor industry as a gate electrode, interconnect material and for various other applications. Small variations in deposition conditions can significantly affect this material's properties, cause errors in metrology control of the film thicknesses and, ultimately, in device performance. In this work polySi was LPCVD deposited in a vertical reactor with multiple gas inlets and a flat temperature distribution. Deposition conditions were controllably changed to create a matrix of wafers. Characterization is done using production dual wavelength, multiple-angle-of-incidence and research grade spectroscopie ellipsometers. PolySi thickness and composition uniformity are analyzed.

The temperature dependence of the silicon dangling-bond resonance in polycrystalline (poly-Si) and amorphous silicon (a-Si:H) was measured. At room temperature, electron paramagnetic resonance (EPR) measurements reveal an isotropie g-value of 2.0055 and a line width of 6.5 and 6.1 G for Si dangling-bonds in a-Si:H and poly-Si, respectively. In both materials spin density and g-value are independent of temperature. While in a-Si:H the width of the resonance did not change with temperature, poly-Si exhibits a remarkable T dependence of ΔHpp. In unpassivated poly-Si a pronounced decrease of ΔHpp is observed for temperatures above 300 K. At 384 K ΔHpp reaches a minimum of 5.1 G, then increases to 6.1 G at 460 K, and eventually decreases to 4.6 G at 530 K. In hydrogenated poly-Si ΔHpp decreases monotonically above 425 K. The decrease of ΔHpp is attributed to electron hopping causing motional narrowing. An average hopping distance of 15 and 17.5 Å was estimated for unhydrogenated and H passivated poly-Si, respectively.

A new kind of Real Time Spectroscopie Ellipsometer (RTSE) system is presented in detail. A multichannel analyser with photointensifier allows one to get spectroscopie measurements over the 0.25–0.85μm wavelength range with resolution λ/Δλ better than 500 and a good signal to noise ratio even for samples with poor reflectance. Precision and reproducibility of the system are around 0.3 and 0.1% for the two ellipsometric parameters. The measurement speed can be increased up to 15 spectra/s but must be adapted accurately to the process under control. An example of the heating process of a GaAs substrate measured in-situ by RTSE is presented and the temperature and native oxide thickness are deduced.

Phosphorus doped boron carbon alloy films were made by chemical vapor deposition from a single source compound, dimeric chloro-phospha(III) carburane ((C2B10H10)2(PCl)2). Phosphorus doped B5C materials exhibit increases in the band gap from 0.9 eV to 2.6 eV.

RhSb3 belongs to a class of solids called skutterudites which were recently identified as promising novel thermoelectric materials. Our intent was to explore thin film growth of RhSb3 and to assess the thermoelectric properties of such films. RhSb3 films were prepared by electron-beam deposition on silicon and sapphire substrates. Thermopower, electrical resistivity and the Hall effect were measured over the temperature range from 2K to 300K. The data are compared to measurements on single crystals of RhSb3.