P. Rava

Optoelectronic properties, structure and composition of a-SiC:H films grown in undiluted and H2 diluted silane-methane plasma

a-SiC:H films with energy gap in the range 2.00–2.65 eV have been grown by plasma enhanced chemical vapor deposition in undiluted and H2 diluted SiH4+CH4 gas mixtures, by making use of optimized deposition conditions. A complete picture of structural, compositional, optoelectronic, and defective properties for high quality films has been drawn for the first time. We show that the addition of H2 to the gas mixture leads to a different chemical composition of the deposited films; in particular, carbon incorporation is enhanced and a carbon fraction in the solid matrix up to C/(C+Si)≈0.45 can be obtained. These films have a higher mass density, a reduced microvoid and carbon cluster concentration, a better structural connectivity, and improved optoelectronic properties. For samples with optical gap below 2.4 eV, the reduced defect concentration of H2 diluted films results in an increase of the photoconductivity gain and the steady-state (ημτ)ss values up to two orders of magnitude.

Optical, structural and electrical properties of device-quality hydrogenated amorphous silicon-nitrogen films deposited by plasma-enhanced chemical vapour deposition

Abstract High-electronic quality hydrogenated amorphous silicon-nitrogen (a-Si1-xNx: H) films with an energy gap in the range 1.9-2.7eV have been deposited by plasma-enhanced chemical vapour deposition in silane-ammonia gas mixtures at two different gas residence times and in hydrogen-diluted silane-ammonia gas mixtures. Compositional, structural, electrical and optical properties have been investigated. For the first time the effects of hydrogen dilution of SiH4 + NH3 gas mixtures on the a-Si1-xNx: H network is reported. We have observed that hydrogen dilution decreases hydrogen incorporation and increases nitrogen incorporation, promoting a higher connectivity of the a-Si1-xNx :H network. All films show good electronic properties, comparable with or superior to those of amorphous silicon-carbon films, which are improved in films deposited from hydrogen-diluted gas mixtures.

Physical Properties of Undoped and Doped Microcrystalline SiC:H Deposited by PECVD

Experimental results on a systematic investigation on the elemental composition, structural, optical and electrical properties of undoped and doped microcrystalline silicon carbide films deposited by Plasma Enhanced Chemical Vapor Deposition. The doped samples show high values of dark conductivity accompanied by good optical properties so to satisfy the requirements for heterojunction window material.

Optimization of a-Si1−xCx: H films prepared by ultrahigh vacuum plasma enhanced chemical vapour deposition for electroluminescent devices

Abstract The correlation between the deposition conditions and the structural and optoelectronic properties of a-SiC:H were studied in order to obtain optimized device-quality films. Two different sets of films were deposited by plasma enhanced chemical vapour deposition, with and without H 2 dilution of the mixture of SiH 4 +CH 4 respectively. An improvement in the optoelectronic properties was observed: the H 2 -diluted films show higher photoconductivity, sharper Urbach energy, reduced sub-band gap absorption and reduced CH n and SiH 2 bond density with respect to undiluted films. The growth mechanisms were interpreted by means of chemical bonding configurations deduced from IR absorptance measurements.

Characterization of the effect of growth conditions on a‐SiC:H films

The effects of dissipated power and gas dwell time in SiH4+CH4 plasmas on the properties of a‐SiC:H films deposited by plasma‐enhanced chemical‐vapor deposition have been investigated for different methane fractions in plasmas operating in the low‐power regime. Optical, structural, and electrical characterizations have been performed in order to investigate the influence of dissipated power and molecule dwell time on the physical properties of a‐SiC:H films. It was found that both the investigated deposition parameters can have a remarkable influence on carbon incorporation and on optical properties such as the energy gap. In particular an increase in the dissipated power or in the molecule dwell time leads to an increase in carbon incorporation and in energy gap. The electrical properties and defect density are still those of device quality films grown in standard deposition conditions and are not influenced by variations in dissipated power or gas dwell time. From these results some conclusions regardin...

Optical properties of hydrogenated amorphous silicon

A detailed study of the optical properties of sputtered hydrogenated amorphous silicon films with varying hydrogen concentration is presented here. The energy dependence of the absorption coefficient is looked into, in detail, from a point of view of understanding the well known Tauc rule and the alternate relations being proposed in recent years. Spectroscopic and band‐structural models like Wemple–Didomenico and Penn are then utilized to analyze the optical parameters near the band‐gap region of the wavelength spectra. Extensive comparisons of our results are made with those of sputtered a‐Si:H films of other workers, glow discharge prepared a‐Si:H, chemically vapor deposited and evaporated a‐Si, and also crystalline silicon. The similarities in the variation of the optical properties of a‐Si:H with increasing hydrogen concentration (or decreasing measurement temperature) to that of crystalline silicon with decreasing measurement temperature lead us to interesting conclusions. Thus, it seems that decrea...

Influence of film thickness on optical and electrical properties of hydrogenated amorphous silicon

Abstract The optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) films produced by magnetron sputtering (SP) and glow discharge (GD) were studied as a function of the film thickness (50–300 nm). A strong dependence on the thickness was observed in the maximum values of the absorption coefficient and in the energy gap Eg (obtained from (αE) 1 2 vs. E plots) for both series. For the SP films the refractive index n(λ) increased with thickness, whereas for GD films e2max and its corresponding energy decreased with increasing thickness. The resistivity values are within the range of typical values for a-Si:H, but no effect of thickness was observed, because of non-uniformity of the films and band bending at the substrate interface.

Properties of a-SiC:H films deposited in high power regime

Abstract The aim of the present paper is the study of the RF power effects on the properties of hydrogenated amorphous silicon-carbon (a-SiC:H) films, deposited in high power regime in a conventional plasma enhanced chemical vapor deposition system by using silane–methane gas mixtures highly diluted in hydrogen. Varying the RF power chemically ordered a-SiC:H alloys can be grown controlling the carbon content, C/[C+Si], and consequently the energy gap from 0.20 to 0.57 and 2.17 to 3.23 eV, respectively. C-rich films show defect density lower than 2×10 17 cm −3 and photoluminescence (PL) at room temperature. The PL peak position of the spectra shifts from 1.70 to 2.54 eV as the carbon content increases from 0.3 to 0.57.

Magnetron Sputtered Amorphous Silicon

The optical properties of undoped α‐Si:H films prepared using magnetron sputtering at different deposition conditions were studied by measuring their transmittance and reflectance between λ=0.25 and λ=1.5 μm and their thickness. The extracted optical constants are interpreted to give values of the band gap. Values of dark conductivity and activation energy are also obtained. The study has been extended to structures SnO2/α‐Si:H/substrate. From measurements of transmittance and reflectance of the system optical constants of the components can be extracted.

Physical properties of amorphous silicon-carbon alloys produced by different techniques

Results of a study of compositional, optical, electrical, and structural properties of hydrogen amorphous silicon carbide (a-SiC:H) prepared, respectively, by glow-discharge (GD) and reactive sputtering (SP) techniques at power densities varying between 1.25 · 10−2 and 1.25 · 10−1 W · cm−2 for GD samples are presented. Measurements are reported on the composition, optical and IR spectroscopy, and on the temperature dependence of electrical conductivity. All experimental observations suggest that the power density only slightly affects the physical properties of GD silicon-rich samples, whereas those of the carbon-rich SP samples depend more strongly on this deposition parameter. Finally, it is shown that the GD technique can provide films with better characteristics, whereas samples of similar composition prepared by sputtering have higher compositional disorder and are more inhomogeneous