This work presents a study on the activation behavior of high-dose (φ > 1015 cm-2) boron and phosphorus implants for low resistance source and drain regions for thin-film transistors (TFTs) fabricated using solid-phase crystallization (SPC) of amorphous silicon. Process variables include factors associated with ion implant and annealing conditions, as well as the SPC and implant process arrangement. Four-point probe sheet resistance (Rs) measurements were used as a comprehensive assessment of the electrical properties. Results have identified similarities and differences in activation behavior that can influence process integration strategies considering both the SPC approach and TFT fabrication.

We report formation of thin silicon oxide films on the silicon surfaces by combination of oxygen radical and high pressure H2O vapor heat treatment for passivation of silicon surfaces at a low temperature. Oxygen plasma was generated by 13.56 MHz radio frequency induction-coupled remote plasma with mixed gases of O2 and Ar at 2 sccm, 2x10-2 Pa and at a power of 50 W. Oxygen radical was produced from the plasma via a metal mesh closing plasma in the reactor. The top surfaces of 20 Wcm n-type silicon substrates with the rear surface coated by thermally grown SiO2 layers were exposed by oxygen radical from 1 to 5 min to oxidize the silicon surface. The samples were subsequently annealed with 9.0x105 Pa H2O vapor heat treatment at 260oC for 3 h. The effective minority carrier lifetime estimated using photo-induced carrier microwave absorption system in the case of 635 nm light illumination at 1.5 mW/cm2 to the top surface increased from 1.3x10-4 to 5.1x10-4s as the oxygen radical treatment duration increased from 1 to 5 min. The recombination velocity decreased from 380 to 90 cm/s. 500 kHz capacitance response with bias gate voltages characteristics of metal oxide semiconductor structure resulted in the effective oxide thicknesses (EOT) ranging from 1.3 to 1.7 nm. These results indicate a capability of thin oxide formation and effective passivation of silicon surfaces at a low temperature.

In this work we present the results of comparative study n- and p-doping of Ge:H and Ge0.96Si0.04 :H films deposited by LF PECVD at high deposition temperature (HT) Td=300°C and low deposition temperature (LT) Td=160°C. The concentration of boron and phosphorus in solid phase was measured by means of SIMS technique. Such parameters as spectral dependence of absorption coefficient, room temperature conductivity σRT and activation energy Ea for both intrinsic and doped films were obtained. The doping range studied in gas phase was for boron [B]gas= 0 to 0.15% and for phosphorus [P]gas= 0 to 0.2%. In general effect of deposition temperature on P and B doping has been demonstrated. For LT films changes of [P]gas=0.04% to 0.22% resulted in more than 2 orders increasing conductivity and reducing activation energy from Ea=0.28 to 0.16 eV. HT films in the range of [P]gas=0.04% to 0.2% demonstrated saturation of conductivity. HT films showed continuous reducing Ea with increase of [P]gas. In the case of boron doping both HT and LT films had a minimum of conductivity at certain values of [B]gas=0.05% (LT films) and 0.04% (HT films) and related maximums of activation energy Ea(max) at the same doping with Ea(max)=0.47 eV for HT and Ea(max)=0.53 eV for LT films. It suggests a compensation of electron conductivity in un-doped films for low B doping. Further raising [B]gas leads to reducing Ea and the smallest Ea=0.27 eV was obtained at [B]gas=0.18% for HT films and Ea=0.33 eV at [B]gas=0.14% for LH films.

Hydrogenated amorphous silicon-germanium alloy thin films (a-Si1-xGex:H) were deposited using reactive magnetron sputtering. Dual targets of silicon and germanium were sputtered in an argon + hydrogen atmosphere using rf excitation. Films with x = 0.4 were deposited as a function of substrate temperature and hydrogen partial pressure, and were evaluated by dark and photoconductivity, infrared absorption, and optical transmission. Photosensitivity reached a maximum value of about 5000 between 150 and 200 °C. Using the stretching modes in the region of 2000 cm-1, the hydrogen bonding was characterized in terms of the preferential attachment ratio (PA), which represents the ratio of H bonded to silicon to that bonded to germanium. The PA shows a systematic increase with increasing temperature, independent of hydrogen partial pressure. The interplay between thermodynamic and kinetics effects in determining PA and film quality will be discussed.

We have carried out in-situ measurements of cluster volume fraction in silicon films during deposition by using quartz crystal microbalances (QCM’s) together with a cluster-eliminating filter. The cluster volume fraction in films is deduced from in-situ measurements of film deposition rates with and without silicon clusters using QCM’s. The results show that the higher deposition rate leads to the higher volume fraction of clusters.

Quantum dot-sensitized solar cells (QDSCs) based on the multiple exciton generation (MEG) of QD are attractive in the field of photochemical cells because the improvement of conventional sensitized solar cells has been stagnant recently. The distinctive characteristics of QDs are their strong photo-response in the visible region and quantum confinement effects. Its theoretical efficiency is much higher than that of solar cell based on the single exciton generation (SEG). Moreover, QDs have tunable optical properties and band-gaps depending on the particle size. But QD materials widely used for QDSC have some disadvantages of toxicity and scarcity. On the other hand, Si as one of good QD materials is abundant and not toxic. Also, Si QD has high stability against light soaking and a high optical absorption coefficient due to quantum size effects. However, the research on Si QD is rare although the quantum effect of Si was already verified. It is one of reasons that the fabrication and collection of Si nano-particles are too difficult. Therefore, this work proposed multi-hollow plasma discharge chemical vapor deposition (CVD). It is possible to collect Si particles unlike conventional CVD and solve the problems of the wet process. The optical properties of Si particles were controlled by varying experimental conditions. In this work, Si particles were fabricated with various sizes and their characteristics were analyzed. Based on the results, Si QD was applied to Si QDSC.

We summarize our research studies on the synthesis of silicon and germanium nanocrystals and their application to the growth of a variety of thin films, spanning the range from fully disordered amorphous up to fully ordered crystalline. All these films are deposited in a standard radio-frequency glow discharge system at low temperature (~200 °C). We show how the plasma synthesis of silicon nanocrystals, initially a side effect of powder formation, has become over the years an exciting field of research which has opened the way to new opportunities in the field of materials deposition and their application to optoelectronic devices. Our results suggest that epitaxy requires the melting/amorphization of the nanocrystals upon impact on the substrate, the subsequent epitaxial growth being favored on (100) c-Si substrates. As a consequence, the control of the impact energy is a critical aspect of the growth which will require new strategies such as the use of tailored voltage waveforms.

We have succeeded in the rapid epitaxial growth of Si, Ge, and SiGe films on Si substrates below 670 ºC by reactive CVD utilizing the spontaneous exothermic reaction between SiH4, GeH4, and F2. Mono-crystalline SiGe epitaxial films with Ge composition ranging from 0.1 to 1.0 have been successfully grown by reactive CVD for the first time.

This technique has also been successfully applied to the growth of these films on silicon-on-glass substrates by a 20 - 50 ºC increase of the heating temperature. Over 10 μm thick epitaxial films at 3 nm/s growth rate are obtained. The etch pit density of the 5.2 μm-thick Si0.5Ge0.5 film is as low as 5 x 106 cm-2 on top. Mobilities of the undoped SiGe and Si films are 180 to 550 cm2/Vs, confirming the good crystallinity of the epitaxial films.

Effusion measurements of hydrogen and implanted helium are reported for (undoped) amorphous and crystalline Si:H and related materials. Effusion of helium observed at temperatures > 600°C is attributed to isolated voids present in the material from the preparation process. While rather high void densities are detected for amorphous silicon films prepared by such deposition techniques like vacuum evaporation or sputtering, much smaller densities are found for plasma grown hydrogenated amorphous silicon (a-Si:H). For device-grade a-Si:H, the density of cavities which can trap helium is estimated to be about 2x1018/cm3at most, suggesting that crystalline silicon type divacancies are not the major hydrogen incorporation site.

P-type hydrogenated nanocrystalline cubic silicon carbide is a promising material for the emitter of n-type crystalline silicon heterojunction solar cell due to its lower light absorption and wider bandgap of 2.2 eV. The electrical properties of hydrogenated nanocrystalline cubic silicon carbide can be influenced by its crystallinity. In this study, we propose the use of conductive atomic force microscopy (Conductive-AFM) to evaluate the crystalline volume fraction (f c) of p-nc-3C-SiC:H thin films (20∼30 nm) as a new method instead of Raman scattering spectroscopy, X-ray diffraction, and spectroscopic ellipsometry.

Change in the light-induced minority carrier effective lifetime τeff of crystalline silicon caused by rapid laser heating is reported. The top surface of n- and p-type silicon substrates with thicknesses of 520 μm coated with thermally grown SiO2 layers were heated by a 940 nm semiconductor laser for 4 ms. τeff was measured by a method of microwave absorption caused by carriers induced by 620 nm light illumination at 1.5 mW/cm2. τeff for light illumination of the top surfaces was decreased to 1.0x10-5 and 4.8x10-6 s by laser heating at 5.0x104 W/cm2 for n- and ptype 520-μm-thick silicon substrates, respectively. The decrease in τeff resulted from the generation of defect states associated with the carrier recombination velocity at the top surface region, S top. Laser heating increased S top to 6000 and 10000 cm/s for n- and p-type silicon samples, respectively. Heat treatment at 400oC for 4h markedly decreased S top to 21 and 120 cm/s, respectively, for n- and p-type silicon samples heated at 5.0x104 W/cm2. Laser heating at 4.0x104 W/cm2 for 4 ms was also applied to samples treated with Ar plasma irradiation at 50 W for 60 s, which decreased τeff (top) to 2.0x10-5 s and 3.9x10-6 s for n- and p-type silicon samples, respectively. Laser heating successfully increased τeff (top) to 2.8x10-3 and 4.1x10-4 s for n- and p-type samples, respectively. Laser irradiation at 4x104 W/cm2played a role of curing recombination defect sites.

In this paper, we report on deposition and properties of nanocrystalline Ge:H films . The films were grown from germane and hydrogen mixtures using Radio frequency Plasma-enhanced chemical vapor deposition (RF-PECVD) process using ∼45 MHz frequency. The crystallinity of the films was measured using Raman measurements and from x-ray diffraction techniques, it was found that the grain size was a strong function of deposition pressure, temperature and hydrogen/germane ratios. High hydrogen ratios and high powers led to films with smaller grains. Higher pressures and smaller hydrogen/germane ratio led to films with larger grain sizes, as did higher growth temperatures. The mobility of electrons and holes was measured using space charge limited current (SCLC) techniques in n+-n-n+ devices. It was found that nominally undoped films were generally n type with carrier concentrations in the 1E14/cm3 range. Mobility was found to increase with grain size, with 60 nm grains showing mobility in the 2-3 cm2/V-s range.

The dark current-voltage characteristics of PIN structures are studied and analyzed for PV samples as for integral device without taking account the performance of the different elements typically used in equivalent circuit model such as diode n-factor, shunt and series resistances. The contribution of all these elements is very important in the development of devices because they determine the performance characteristics. In this work we have studied and compared the temperature dependence of current-voltage characteristics in μc-Si:H and pm-Si:H p-i-n structures having approximately the same efficiencies with emphasis on their different electronic characteristics such as shunt (Rsh) and series (Rs) resistance, ideality factor (n), and the saturation current (Is), which give us some ideas on role of these elements. In the pm-Si:H cell it was observed that the Rs increases with the increase of the temperature in contrast to the μc-Si:H structures, where the series resistance reduces with temperature change from T = 300 up to 480K. In both the pm-Si:H and μc-Si:H samples Rshreduces with temperature change from 300 up to 480 K. The ideality factor in the pm-Si:H structure shows an increase, and in μc-Si:H a reduction, when temperature increases. Saturation current in both cases increases with temperature as it was expected. From the saturation current it was obtained the build-in potential. Analysis behavior of both saturation current and n-factor with temperature shows that build-in potential increases with temperature in the pm-Si:H, but reduces in μc-Si:H structure.

We report on a direct measurement of electrical potential and field profiles across the n-i-p junction of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells, using the nanometer-resolution potential imaging technique of scanning Kelvin probe force microscopy (SKPFM). It was observed that the electric field is nonuniform across the i layer. It is much higher in the p/i region than in the middle and the n/i region, illustrating that the i layer is actually slightly n-type. A measurement on a nc-Si:H cell with a higher oxygen impurity concentration shows that the nonuniformity of the electric field is much more pronounced than in samples having a lower O impurity, indicating that O is an electron donor in nc-Si:H materials. This nonuniform distribution of electric field implies a mixture of diffusion and drift of carrier transport in the nc-Si:H solar cells. The composition and structure of these nc-Si:H cells were further investigated by using secondary-ion mass spectrometry and Raman spectroscopy, respectively. The effects of impurity and structural properties on the electrical potential distribution and solar cell performance are discussed.

We have developed a cluster-eliminating filter which reduces amount of amorphous silicon nanoparticles (clusters) incorporated into a-Si:H films. We have applied the filter to fabricate a-Si:H Schottky solar cells. The cells show a high initial fill factor FF=0.563 and a high stabilized value after light soaking FF=0.552 which light-induced degradation was quite low value of 1.95 %.

We investigate the influence of the crystallinity of the absorber layer and parasitic absorption in the doped layers and electrodes on the external quantum efficiency and reflection of microcrystalline silicon (μc-Si:H) solar cells. Using an optical light scattering model we systematically study variations in the crystallinity and validate a simple normalization procedure that allows assessing the gains that can be achieved by reducing the parasitic absorption. The optimization potential is demonstrated with solar cell samples with increased crystallinity and eliminated parasitic absorption.

In this paper, we present experimental findings pertaining to the formation of twins in isolated single-crystal islands obtained via the dot-SLS method. Systematic characterization of the islands using EBSD reveals that Σ = 3 CSL twins constitute the predominant extended defect. Given this, the surface orientation of the seed and twinned regions are shown to be related by a 180° rotation about a <111> axis, and the orientation of the twinned area is apparently manifested in the inverse pole figure as a reflection across the {112} zone. By considering (1) the overall pattern of the twin boundaries within the islands, (2) that solidification proceeds via a facetted mode of growth and, (3) that intragrain-defect-free regions were obtained when the dot-SLS process was performed on a {100} surface-oriented seed, we suggest that these twins are most likely generated heterogeneously at the Si/SiO2interface during the ledge nucleation stage of rapid lateral solidification of the films.

We present a femtosecond pump-probe ellipsometer operating over a spectral range of 1.4 – 1.7 eV with a ∼50fs time resolution. The calibration and preliminary findings of the setup are discussed. We tested the apparatus on bulk crystalline silicon (not shown here) and on silicon nanocrystals embedded in an amorphous silicon phase. The ellipsometric angles (ψ, Δ) were determined as a function of time and wavelength. The results suggest that a simple Drude model of free carrier absorption is not sufficient to explain the findings.

A one-dimensional model has been developed for radio frequency (RF) glow discharge of SiH4/GeH4/H2 3-gases mixture at a high pressure regime based on the fluid model. The behavior of electrons, neutrals, radicals and ions with corresponding rate constants is described by driftdiffusion equations that are coupled with the Poisson’s equation and solved with an explicit central-difference discretization scheme. The germanium (Ge) content in the deposited film and germane (GeH4) radical fraction in the gas phase are found to decrease as total gas pressure increases in contrast to the increased deposition rate, which are explained by the fact that GeHx-group species are more thoroughly depleted and less promoted by the denser plasma at high pressure compared to SiHx-group species. The multiplied population of electrons and hydrogen atoms in the quadratically denser plasma also boosts secondary reactions which are favorable for SiH3 and GeH3 and consume SiH2 and GeH2for high order radicals.

Amorphous silicon-germanium (a-Si0.01Ge0.99:H) thin film, practically amorphous germanium with small concentration of silicon, were deposited by the low frequency PECVD technique under different flow gas of phosphine in the range of QPH3 = 20 to 100 sccm. In this range the phosphorous concentration in gas phase was calculated as XP= 4 to 20 % which resulted in a content in solid phase [P]sol=0.12% - 0.4%. The P content of the solid phase was measured by SIMS profiling and it was also observed a preferential incorporation of phosphorous in the range of [P]sol=0.12% - 0.3%. Hydrogen concentration in the films was determined from FTIR and SIMS measurements. The activation energy was determined by measuring the temperature dependence of conductivity in DC regime in a vacuum thermostat. For the a-Si0.01Ge0.99:H films it is found that the activation energy have a minimum, (Ea= 0.15eV), its conductivity at room temperature have a maximum and there is a minimum of of both band tail and deep localized state for a phosphorous incorporation in solid phase [P] =0.28%.