Hydrogenated amorphous silicon carbide (a-SiC:H) can provide exceptional surface passivation essential for high-efficiency crystalline silicon solar cells. This thesis reports on the fundamental study of a-SiC:H films deposited using a novel deposition technique, DC saddle field PECVD, in contrast to the conventional industrial use of RF-PECVD. The growth conditions were optimized and correlated with passivating, structural, and optical characteristics. The lifetime has a strong dependency on deposition temperature and improves by over two orders of magnitude as the temperature increases; the maximum lifetime achieved in this work reached 0.5 ms. In addition, the Tauc optical gap can be increased from 1.7 eV to 2.3 eV by varying the precursor gas mixture ratio. Post-deposition annealing experiments demonstrate thermal stability of the samples deposited at 250 °C and in some instances shows improvement in passivation quality by a factor of two with a one-step annealing treatment at 300 °C for 15 minutes.

Abstract Silicon carbide is a versatile material amenable to variety of applications from electrical insulation to surface passivation, diffusion-barrier in optoelectronic and high-frequency devices. This research presents a fundamental study of a-SiC:H films with variable stoichiometries deposited using novel technique, DC saddle-field plasma-enhanced chemical-vapour deposition, a departure from conventional RF PECVD commonly used in industry. DCSF PECVD is an alternative technique for low temperature large area deposition. Stoichiometric a-SiC:H obtained by fine-tuning precursor gas mixture. Annealing up to 800oC showed no significant change in elemental composition; particularly indicating thermal stability at stoichiometry. Ellipsometry showed wide range of optical gaps whose maximum surpasses values reported in literature. Refractive index measured and change in values studied as function of increasing carbon content in the films. Also attainment of very smooth surface morphology for stoichiometric a-SiC:H films reported. Surface roughness of 1 nm rms demonstrated for films grown at temperature as low as 225oC.

Hydrogenated amorphous silicon carbide (a-SiC:H) can provide exceptional surface passivation essential for high-efficiency crystalline silicon solar cells. This thesis reports on the fundamental study of a-SiC:H films deposited using a novel deposition technique, DC saddle field PECVD, in contrast to the conventional industrial use of RF-PECVD. The growth conditions were optimized and correlated with passivating, structural, and optical characteristics. The lifetime has a strong dependency on deposition temperature and improves by over two orders of magnitude as the temperature increases; the maximum lifetime achieved in this work reached 0.5 ms. In addition, the Tauc optical gap can be increased from 1.7 eV to 2.3 eV by varying the precursor gas mixture ratio. Post-deposition annealing experiments demonstrate thermal stability of the samples deposited at 250 °C and in some instances shows improvement in passivation quality by a factor of two with a one-step annealing treatment at 300 °C for 15 minutes.

Abstract Silicon carbide is a versatile material amenable to variety of applications from electrical insulation to surface passivation, diffusion-barrier in optoelectronic and high-frequency devices. This research presents a fundamental study of a-SiC:H films with variable stoichiometries deposited using novel technique, DC saddle-field plasma-enhanced chemical-vapour deposition, a departure from conventional RF PECVD commonly used in industry. DCSF PECVD is an alternative technique for low temperature large area deposition. Stoichiometric a-SiC:H obtained by fine-tuning precursor gas mixture. Annealing up to 800oC showed no significant change in elemental composition; particularly indicating thermal stability at stoichiometry. Ellipsometry showed wide range of optical gaps whose maximum surpasses values reported in literature. Refractive index measured and change in values studied as function of increasing carbon content in the films. Also attainment of very smooth surface morphology for stoichiometric a-SiC:H films reported. Surface roughness of 1 nm rms demonstrated for films grown at temperature as low as 225oC.

>Magister Scientiae - MSc / Amorphous silicon carbide (a-SiC) is a versatile material due to its interesting mechanical, chemical and optical properties that make it a candidate for application in solar cell technology. As a-SiC stoichiometry can be tuned over a large range, consequently is its bandgap. In this thesis, amorphous silicon carbide thin films for solar cells application have been deposited by means of the electron-beam physical vapour deposition (e-beam PVD) technique and have been isochronally annealed at varying temperatures. The structural and optical properties of the films have been investigated by Fourier transform Infrared and Raman spectroscopies, X-ray diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and UV-VIS-NIR spectroscopy. The effect of annealing is a gradual crystallization of the amorphous network of as-deposited silicon carbide films and consequently the microstructural and optical properties are altered. We showed that the microstructural changes of the as-deposited films depend on the annealing temperature. High temperature enhances the growth of Si and SiC nanocrystals in amorphous SiC matrix. Improved stoichiometry of SiC comes with high band gap of the material up to 2.53 eV which makes the films transparent to the visible radiation and thus they can be applied as window layer in solar cells.

The fundamentals of the ellipsometry are reviewed in order to point out the strengths and weaknesses of the ellipsometric measurements. The effects of the surface conditions (such as degree of cleanliness, contaminated thin layer, roughness etc&hellip / ) on the ellipsometric variables are experimentally studied / the optimum procedures have been determined. Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) thin films are produced by plasma enhanced chemical vapor deposition (PECVD) technique with a circular reactor, in a way that RF power and carbon contents are taken as variables. These samples are analyzed using multiple angle of incidence ellipsometer and uv-vis spectrometer. These measurements have inhomogeneities in optical constants, such as thicknesses, refractive indices and optical energy gaps along the radial direction of the reactor electrode for different power and carbon contents.

The structure and the energy band gap of hydrogenated amorphous silicon carbide are theoretically revised. In the light of defect pool model, density of states distribution is investigated for various regions of mobility gap. The films are deposited by plasma enhanced chemical vapor deposition system with various gas concentrations at two different, lower (30 mW/cm2) and higher (90 mW/cm2), radio frequency power densities. The elemental composition of hydrogenated amorphous silicon carbide films and relative composition of existing bond types are analyzed by x-ray photoelectron spectroscopy measurements. The thicknesses, deposition rates, refractive indices and optical band gaps of the films are determined by ultraviolet visible transmittance measurements. Uniformity of the deposited films is analyzed along the radial direction of the bottom electrode of the plasma enhanced chemical vapor deposition reactor. The molecular vibration characteristics of the films are reviewed and analyzed by Fourier transform infrared spectroscopy measurements. Electrical characteristics of the films are analyzed by dc conductivity measurements. Conduction mechanisms, such as extended state, nearest neighbor and variable range hopping in tail states are revised. The hopping conductivities are analyzed by considering the density of states distribution in various regions of mobility gap. The experimentally measured activation energies for the films of high carbon content are too low to be interpreted as the difference between Fermi level and relevant band edge. This anomaly has been successfully removed by introducing hopping conduction across localized tail states of the relevant band. In other words, the second contribution lowers the mobility edge towards the Fermi level.

Notre étude concerne la mise en place et le développement de dépôts de carbure de silicium amorphe hydrogéné (a-SiCx:H) à basse température (370°C), par voie PECVD, sur un réacteur PECVD semi-industriel à faible fréquence (440 kHz). Les propriétés chimiques, optiques et de passivation de surface des couches déposées sont analysées et l’impact du changement des débits de gaz précurseurs (silane et méthane) est aussi étudié. La possibilité d’utiliser le a-SiCx:H comme couche anti-reflet en face avant d’une cellule solaire est envisagée. Bien que l’indice de réfraction d’une couche riche en carbone soit en accord avec la condition de lame quart-d’onde requise pour une couche anti-reflet, le coefficient d’extinction est trop élevé en raison de la proportion significative de silicium dans la couche. Cette absorption peut être atténuée par l’incorporation d’azote dans la couche (a-SiCxNy:H). En revanche, la passivation de surface s’améliore lorsque la quantité de silane augmente. La plus faible vitesse de recombinaison de surface atteinte sur les échantillons après dépôt est de 10 cm.s. / Our study deals with the deposition of amorphous hydrogenated silicon carbide (a- SiCx:H) at low temperature (370°C), by PECVD technique, using a semi-industrial lowfrequency PECVD reactor (440 kHz). The deposited films are analyzed for chemical, optical and surface passivation properties, and the impact of the gas flow parameters (silane and methane) is studied. The possible use of a-SiCx:H as an antireflective coating at the front side of solar cells is investigated. Although the refractive index for high carbon concentration could be in agreement with the demand of quarter-wave layer for antireflective coating, the extinction coefficient remains too high due to a significant silicon content in the material. This absorption can be attenuated by incorporating nitrogen in the layer. However, the surface passivation improves with the silane proportion. The lowest surface recombination velocity of an as-deposited samples is about 10 cm.s.