Periodically aligned submicron Si dots were fabricated by only irradiating linearly polarized Nd:YAG pulse laser to the amorphous silicon (a-Si) thin film deposited on silicon dioxide (SiO2) film. Interference between the incident beam and the scattered surface wave leads to the spatial periodicity of beam energy density distribution on the surface of the irradiated samples. The a-Si thin film was melted by laser beam, and then, the molten thin Si film was split and condensed due to its surface tensile according to the periodic energy density distribution. The polycrystalline Si (poly-Si) fine lines were formed periodically. After the first irradiation, the sample was rotated by 90o, and the laser beam was irradiated. The periodic energy density distribution was generated on the Si fine lines. Then, the lines were split off and condensed according to the periodic energy density distribution, and the periodically aligned submicron Si dots were fabricated on the SiO2 film.

We used a polycrystalline YSZ film deposited on the quartz substrate as a seed layer to enhance crystallization of the Si film deposited on it. The YSZ film was deposited by reactive sputtering at less than 50°C and the preferential orientation was (111). The 60-nm-thick Si film was deposited by e-beam evaporation method on the substrate with and without the YSZ film. It was found that the crystallization of the Si film deposited on the YSZ film occurs but not without the YSZ film at the temperature of 515°C. The SEM image of the Secco-etched Si film showed that the crystallized Si film consisted of ~50-nm-size grains and, from the TEM image, it is supposed that the Si grains are grown directly from the YSZ film.

A thin-film amorphous silicon (a-Si) deposited on a glass substrate was employed as a semiconductor material for the chemical imaging sensor, which can visualize the distribution of ion concentration in a solution. The sensing properties and the spatial resolution of the a-Si sensors were investigated. Nearly-Nernstian pH sensitivities and submicron resolution were demonstrated, which suggests the superior performance of the chemical imaging sensor based on thin-film a-Si.

A number of a-Si:H samples prepared in an expanding thermal plasma under varying conditions were examined by means of time-of-flight transient photocurrent measurements. A high deposition temperature allows high deposition rates while achieving high hole mobility and mobility-lifetime product. Lower hole mobility but higher μτ product result from slower deposition at lower temperature. Electron μτ products are uncharacteristically low for all samples due to pronounced deep trapping. RF biasing of the substrate does not improve the results.

We have constructed a hot wire assisted ECR-CVD system to prepare a-Si:H and μc-Si:H films. The effect of hot wire temperature on crystallization of a-Si:H films is studied in the films prepared by these system. The crystalline fraction and crystalline grain size are analyzed by Raman scattering. The hydrogen content and the bonding scheme of hydrogen were measured by Fourier transform infrared (FTIR) spectroscopy. At low hot wire temperature, about 20 at.% hydrogen is included in the film. With increasing the hot wire temperature, the total content of the hydrogen, SiH2 and SiH decrease and the microcrystalline phase appears. It is found from the ratio of the crystalline TO peak to the total area of the TO peak of the Raman scattering spectra that the volume fraction of the crystalline phase increases with increasing the hot wire temperature. The crystalline peak has a tendency to shift toward the higher wavenumber with increasing the hot wire temperature, suggesting that the grain size increases with increasing the hot wire temperature.

A series of boron doped polycrystalline silicon were produced using step-by-step laser crystallization process from amorphous silicon. The influence of doping concentrations on laser- induced dehydrogenation and crystallization of amorphous silicon and on hydrogen bonding have been investigated employing Raman spectroscopy and hydrogen effusion measurements. From hydrogen effusion spectra the hydrogen chemical potential is determined as a function of hydrogen concentration, which can be related to the hydrogen density-of-states distribution. The results from hydrogen effusion are consistent with the results obtained from Raman spectroscopy.

The production of hydrogenated amorphous silicon films containing silicon nanocrystal-line inclusions (a/nc-Si:H) is demonstrated using a new deposition process. Crystalline Si nanoparticles around 5 nm in diameter are generated in a flow-through plasma reactor, and are introduced into a downstream capacitively-coupled plasma enhanced chemical vapor deposition reactor where the particles are “co-deposited” with the amorphous phase of the film. Transmis-sion electron microscopy confirms the presence of crystalline inclusions in these films, as well as providing confirmation that the crystalline particles are indeed produced in the flow-through re-actor and not in the capacitive plasma. Electrical measurements indicate an improvement in the dark conductivity of the intrinsic a/nc-Si:H films as the particle concentration is increased, sug-gesting that the particles have a doping effect on the films charge transport properties.

The concentration of polysilane chains (SiH2)n, where n≥1, is estimated for higher quality hydrogenated amorphous silicon (a-Si:H) by pulsed proton nuclear magnetic resonance techniques (1H NMR). Our measurements indicate the minimum hydrogen content of approximately 10% of the total hydrogen is in the (SiH2)n configuration. Similar measurements in a high defect density sample (1017 silicon dangling bond defects cm-3) show that (SiH2)n sites account for ~ 15% of the total hydrogen. While the (SiH2)n infrared absorption (IR) modes are observed in the highly defective sample, no such modes are seen in the higher quality material. The results indicate that a significant amount of the total hydrogen content exists as (SiH2)n regardless of film quality.

Nanocrystalline p-type Si:H layers are important for photovoltaic and MOSFET devices. A high conductivity in these layers leads to better voltages in PV devices and to lower series resistance in both PV and MOSFET devices. The lower resistance results in higher channel mobility in MOSFET devices and higher fill factors in PV devices. In this work, we discuss the improvement in conductivity and crystallinity of p-type nanocrystalline Si:H layers by the use of post-deposition annealing. The p layers were deposited at ~ 180C from mixtures of silane, hydrogen, helium and diborane using ECR plasma deposition techniques. It was found that addition of He to H at first improved both the conductivity and crystallinity, but too much He led to an amorphous phase and lower conductivity. The as-grown films were measured for their crystallinity using both Raman spectroscopy and x-ray diffraction. The conductivity and activation energies were also measured. The films were then successively annealed at temperatures of 250, 300, 350 and 400C. The crystallinity and grain size were found to increase as the annealing temperature increased. The greatest relative increase was during the initial annealing stages. The conductivity of the films increased significantly as a consequence of the annealing. Conductivities as large as 20 S/cm were obtained in very thin films (~50-150 nm). The corresponding activation energies were in the range of 0.03 eV. When these annealed layers were used for MOSFET and PV devices, there was an appreciable increase in performance characteristics.

In this study, the amorphous-phase roughening transition thickness has been determined as a function of process variables in plasma-enhanced chemical vapor deposition (PECVD) of hydrogenated amorphous silicon-germanium alloys (a Si1-xGex:H). Among the process variables include the H2-dilution gas flow ratio, the alloying flow ratio, the electrode configuration (anode vs. cathode), and the He-dilution ratio. One clear feature of this study is a maximum in the amorphous roughening transition thickness (and hence surface stability) at a H2-dilution ratio just below the transition from amorphous to mixed-phase (amorphous+microcrystalline) (a+μc) growth. A second feature for high Ge content films is a significant increase in the roughening transition thickness for cathode PECVD (with a self-bias of ~ −20 V) relative to anode PECVD. Additional features of interest involve suppression of the mixed-phase transition to (a+μc) for (i) alloying with Ge, (ii) cathodic substrate biasing, and (iii) diluting the gas with He. The close correlation of high surface stability with enhanced short-range order and overall electronic performance has led to a simple model for the transition in terms of a competition between roughening due to the atomic size and smoothening due to precursor surface diffusion. It is proposed that diffusing precursors are immobilized by surface defects (or by other diffusing precursors), and the pre-existing (or resulting) defects are ultimately incorporated in the bulk.

Microcrystalline silicon germanium films (μc-SiGe) were fabricated on Corning #7059 glass substrates by the RF reactive magnetron sputtering method. The μc-SiGe films with Ge fraction of 0.7-0.8 could be crystallized at of 200 °C by H2 introduction into the sputtering gases. The absorption coefficients of the films decrease in long wavelength region corresponding to the photon energies below the energy gap by the decrease in the substrate temperature and become close to those of single crystal Si0.25Ge0.75. The dark conductivities show lower values of 10-7 S/cm at 200 °C and 300 °C with H2 introduction. Besides, the photosensitivities are observed in these samples. These results indicate that the H2 introduction into the sputtering gas has two important effects to decrease the crystallization temperature of the μc-SiGe and to improve the film properties by reducing the dangling bond defects.

A SPICE model of a-SiC:H/ a-Si:H pin/pin detector with voltage controlled spectral sensitivity is presented. The equivalent electric circuit able to describe the behavior of the multilayer structure under non-uniform illumination is composed of two series connected diodes, representing the pin structures, with two nonlinear current sources in parallel, representing the photogeneration for different steady state RGB illumination, with their value depending also on the thickness of the absorber layer and the built-in potential of the diodes. This device represents the 1D model of the LSP (Laser Scanned Photodiode) and may be interconnected in a 2D array trough resistors, modeling the high resistivity of the a-SiC:H layers. Electrical simulations were performed for different transducer configurations and illumination conditions and compared with the experimental data. The influence of the lateral and transverse resistors and built-in potential of the diodes on sensor parameters like spatial resolution, and signal amplitude are analyzed. A physical model supported by the electrical simulation gives insight into the methodology used for image representation and color discrimination.

We report on the growth and properties of p-channel nanocrystalline Si thin film transistor (TFT) devices. In contrast to previous work, the devices are fabricated in n-body nanocrystalline Si. The doping of the n-body is systematically changed by doping with ppm levels of phosphorous. The threshold voltage was found to change systematically as phosphorus content increased. The TFT devices are of the bottom-gate type, grown on oxidized Si wafers. Source and drain contacts were provided by using either plasma grown p type nanocrystalline layers, or by the simple process of Al diffusion. A top layer of plasma-deposited silicon dioxide was found to decrease the off current significantly. High on-off current ratios exceeding 106 were obtained. Hole mobilities in the devices were consistently good, with the best mobility being in the range of ~1.3 cm2/V-s.

The electronic properties of working nanocrystalline silicon (nc-Si:H) solar cell devices with conversion efficiencies up to 8.6% were studied using junction capacitance methods. The set of devices examined were deposited on both specular stainless steel substrates and Ag/ZnO textured back reflectors. These devices included nc-Si:H grown under constant H2 dilution, and also with profiled H2 dilution to control the crystallite sizes and volume fraction. Transient photocapacitance and transient photocurrent spectroscopies were used to obtain sub-band-gap optical spectra. A comparison of these two kinds of spectra also allowed us to deduce the minority carrier collection fractions as a function of temperature and light-induced degradation. Light-soaking was found to cause a distinct decrease in minority carrier collection, as well as a consistent decrease in defects responding to drive-level capacitance profiling. A tentative microscopic model is proposed that accounts for these degradation effects in nc-Si:H.

The nc-Si films where the troublesome incubation layer was almost eliminated were deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) under various dilution conditions. The nc-Si films were analyzed with cross-sectional high resolution transmission electron microscopy (HR-TEM) images. It was verified that the Si crystalline components formed and grew from the surface of buffer layer. The grain size of 20~50nm was measured. The absence of incubation layer in nc-Si film may be attributed mainly to ICP-CVD which generates remote plasma of high density, the role of hydrogen, and the dilution effect on the growth of crystalline. Our experimental results show that incubation-free nc-Si film deposited by ICP-CVD may be suitable for the active layer of bottom gate nc-Si TFTs as well as top gate nc-Si TFTs.

The use of transient photoconductivity techniques in the investigation of carrier transport in microcrystalline silicon is described. Results are presented which highlight variations in transport parameters such as carrier mobility and density of states with structure composition. Hole mobility is significantly enhanced by crystalline content in the film of 10% or less. The density of states inferred from transport measurements parallel to and at right angles to the direction of film growth differ somewhat, suggesting that transport may be anisotropic.

Laser crystallization of silicon thin films on inexpensive glass substrates with a photo-absorption layer of diamond like-carbon (DLC) film was investigated. Scanned near-infrared beam emitted from a continuous wave (CW) laser diode at speed of 30 cm/s with power density of 30 kW/cm2 and wavelength of 940nm was effectively absorbed by DLC films, and changed to thermal energy for heating underlying silicon films with thickness of 50 nm. As a result, crystallization of silicon films was achieved. Raman scattering spectra was measure for the structural analysis of silicon films, and the sharp TO phonon peak at wave number of 520 cm-1 was observed. It shows that silicon films were effectively crystallized using the near-infrared laser diode. On the other hand, no crystallization was observed when the laser diode was directly irradiated to 50-nm-Si/quartz, because silicon has no optical absorption coefficient at 940 nm.

Thin poly-crystalline silicon films are attractive for the fabrication of active matrix liquid crystal displays. We investigate the use of flash lamp annealing to crystallize amorphous silicon layers on glass substrates as a low cost manufacturing route. In this process amorphous silicon (a-Si) can be crystallized by solid phase crystallization (SPC) or in the super lateral growth (SLG) regime. We present a thermal model incorporating the phase transitions during annealing; providing a valuable tool for optimizing the process conditions. Another consideration is the evolution of stress resulting from the transient thermal loading of the substrate material. Results are presented for various substrate geometries and important scalability issues are addressed.

The growth of thin-film silicon close to the amorphous/microcrystalline transition is qualitatively described by a 3D - discrete dynamical growth model on a cubic lattice. The result of this simulation is a representation of the microstructure of the layer as a function of time, i.e. computer-generated animations of growing microcrystalline silicon layers. It permits to follow the evolution of the nucleation and of the growth of the crystalline phase, the surface roughness, the average crystalline volume fraction and the void volume fraction. In these computer simulations, the effects of the substrate surface morphology and of the distribution of particles incidence angle have been studied.

Comparison between simulated normal and isotropic incidence on structured substrates indicates that, under microcrystalline growth conditions, shadowing effects lead to the occurrence of cracks in the simulated microstructure. These effects are also evidenced experimentally in the case of μc-Si:H silicon layers deposited by very high frequency plasma-enhanced chemical vapour deposition (VHF-PECVD) on periodic and random nanostructured substrates.

Low- and high-frequency modulated photoconductivity measurements (LF and HF MPC) have been made on amorphous silicon films prepared by the expanding thermal plasma (ETP) and RF PECVD techniques. Time constants have been measured by decay of square wave excitation and behavior of complex frequency response. The influence of quasi-Fermi level position has been examined. Band tail slopes of 32 meV (ETP) and 37 meV (PECVD), and defect densities of order 1018 and 1017 cm-3 eV-1 respectively are found. Tail state capture coefficients of order 3×10-8 cm3 s-1 are calculated from overlapping LF and HF regimes. Defect state values for ETP (< 10-8 cm3 s-1) are smaller than for PECVD silicon films (> 10-7 cm-3 s-1).