Silicon Deposition on 3C-SiC Seeds of Different Orientations

Silicon deposition on 3C-SiC seeds was studied as a function of seed orientations and thicknesses. The 3C-SiC seeds were grown on silicon substrates of (100), (110), (111) and (211) orientations by standard two-step CVD (low temperature carbonization followed by high temperature epitaxy). Then, the Si layers were grown onto these SiC seeds at various temperatures. Almost all the conditions gave polycrystalline deposit. At high deposition temperature (1350°C) the Si deposit was composed of separated hillocks and was never fully covering the 3C-SiC seeds. Lower deposition temperatures (≤ 1100°C) allowed obtaining silicon full coverage but not full epitaxy. Focusing on (100) orientation, it was shown that (100) Si deposit could be obtained but only on the as carbonized 3C-SiC sample, i.e. with the thinner SiC layer.

Influence of hydrogen concentration on void-related microstructure in low hydrogen amorphous and crystalline silicon materials

The influence of implanted hydrogen (up to a concentration level of 3 at. %) on the microstructure of silicon (Si) materials is investigated by Fourier transform infrared spectroscopy as well as by effusion of hydrogen and of (low dose) implanted helium. Three materials of low original hydrogen concentration, crystalline Si, electron beam evaporated amorphous Si, and plasma-deposited hydrogenated amorphous Si (using high deposition temperature) were investigated. Significant differences between crystalline and amorphous materials were observed. In crystalline Si, implanted hydrogen is found to generate multivacancies that trap diffusing helium while this is not the case in amorphous Si. Accordingly, cavities where hydrogen is located in amorphous Si must be smaller than divacancies. Those cavities in amorphous Si, present from the growth process, that trap helium tend to disappear when the implanted hydrogen concentration increases. Annealing of the materials up to temperatures of 575 °C was also studied. No significant change in the density of voids (trapping helium) occur but in case of crystalline Si the bonding sites of hydrogen as well as the diffusion paths of helium change.

Influence of CVD Parameter on Structure of Graded SiC-C Coating

The influence of chemical vapor deposition process parameters including carrier gas composition, deposition temperature, and content of reactants on the structure of graded SiC-C coating is discussed on the basis of thermodynamic calculation in this paper. The addition of enough hydrogen into carrier gas is necessary for the fabrication graded SiC-C coating. The increase of deposition temperature benefits the control of composition in graded coating but the concentration of free Si and free C becomes high at a too high deposition temperature. A high concentration of reactants is preferred while more defects are apt to exist in coatings if the concentration of reactants is too high. The optimum CVD process parameters for graded SiC-C coating are: gradually changing the molar ratio of SiCl4 and CH4 from 0 to 1 when the concentration of CH4 in hydrogen is 1-2 vol%, and the deposition temperature is 1200-1500 °C.

Comparison of Doping of Gey Si1-y:H (y>0.95) Films Deposited by Low Frequency PECVD at High (300°C) and Low (160°C) Temperatures

ABSTRACTIn 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.

PREPARATION OF NANOCRYSTALLINE SILICON CARBIDE FILMS WITH HIGH SEEBECK COEFFICIENT AND LOW RESISTIVITY

Nanocrystalline silicon carbide ( SiC ) thin films with 5 ~ 10 nm grain size, large Seebeck coefficient (-0.393 mV/K), and low electrical resistivity (3.2 ×10-4 Ohm-m) have been successfully prepared on oxidized silicon substrates by magnetron sputtering of SiC and Al targets. It was found that the addition of a small amount of Al into the SiC film, the high deposition temperature (760 K), and the high thermal annealing temperature (1063 K) were necessary to achieve the goal. The Seebeck coefficient versus logarithm of temperature in the temperature range 383 K to 533 K was a straight line with a slope of -0.999 mV/K. The value of 0.999 mV/K is much larger than the theoretical value of 0.129 mV/K for conventional semiconductors.

The Study of Boron-Doped Nanocrystalline Silicon Film with High Conductivity

Boron-doped nanocrystalline silicon film was prepared through plasma enhanced chemical vapor deposition (PECVD) on silicon substrate and glass substrate under the high deposition pressure (332.5-399Pa) and the high deposition temperature (320-360°C). The film was investigated by Raman, electron probe microanalyser, conductivity and mobility experimenting techniques. The conductivity of the boron-doped nanocrystalline silicon film was 2.97×102Ω-1cm-1. The results showed that the interface between the film and the silicon substrate might have quantum spot and small size effect, causing the increasing of conductivity.

The Influence of Deposition Conditions on the Electronic Properties of a-Si:H Prepared in Expanding Thermal Plasma

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.