Amorphous Silicon Carbon Alloy Films Research Articles

Effect of hydrocarbon gas on the properties of magnetron sputtering of amorphous SiC:H

Hydrogenated amorphous silicon carbon alloy films have been prepared by magntron sputtering of silicon in hydrocarbon-argon gas mixtures. Dependence of the film properties on the ratio, p, of the partial pressure of hydrocarbon gas to the total gas pressure has been investigated, from a viewpoint of the effect of the type of hydrocarbon gas: ethane and methane. With increasing p, the concentration of carbon and the number of carbon-related bonds increase, accompanying an increase in the optical bandgap and the activation energy of dark conductivity. The increasing rate of these quantities against p is smaller for ethane than for methane. The photoconductivity in the case of ethane holds a high value in a wide range of p, compared with the case of methane. This high value is ascribed to the simple configurations of carbon-related bonds deduced from the results of IR absorption.

Midgap-state profiles in undoped amorphous-silicon-based alloys

Abstract Midgap-state densities and profiles in undoped hydrogenated amorphous silicon (a-Si: H), silicon-germanium alloy (a-Si1−x Gex: H) and silicon-carbon alloy (a-Si1−xCx:H) films were obtained from a heterojunction-monitored capacitance method. These midgap states were found to correspond to singly-occupied dangling bonds. The density of midgap states increases slowly with the Ge content in the film, while it increases rapidly with the C content. The peak of the midgap-state profile appears clearly in a-Si:H and a-Si1−xGex:H, bit it does not appear clearly in a-Si1−xCx:H.

Electron energy-loss study of bonding in amorphous silicon-carbon alloy films prepared with hydrogen dilution

Electron energy-loss spectroscopy was used to study the nature of chemical bonding in a-Si1−xCx:H films produced by rf glow discharge decomposition of SiH4/CH4 mixtures with hydrogen dilution. The low-loss region, the Si L edge, and the C K edge were studied. It was found that near stoichiometric films have a high degree of Si to C bonding and that substoichiometric films show some C to C sp2 bonding. A free-electron model was used to interpret the variation of plasmon energy of these films with composition.

Thermally induced metastable defects in hydrogenated amorphous silicon and silicon-carbon alloy films

Thermally induced metastable defects in hydrogenated amorphous silicon and silicon-carbon alloy films

Thermal equilibrium process in undoped hydrogenated amorphous silicon and silicon-carbon alloy films

We find the thermally induced defects in undoped hydrogenated amorphous silicon carbon (a-Si1−xCx:H) by electron spin resonance and conductivity measurements. The equilibrium temperature (Te) determined from the annealing temperature-dependent density of dangling bonds after fast cooling decreases with increasing C content, from 190 °C for hydrogenated amorphous silicon to 150 °C for a-Si0.82C0.18:H. Possible microscopic mechanisms for the observed thermally induced defects in a-Si1−xCx:H alloys are discussed.

Electron spin resonance of hydrogenated amorphous silicon-carbon alloy films prepared by magnetron sputtering

Abstract New electron spin resonance (ESR) lines with g1 = 2·0017 and g2 and g3 = 2·0006 have been found in the ESR spectra of as-deposited a-Si1–x Cx:H films prepared by magnetron sputtering of silicon in the gas mixtures of methane and argon. Similarities between the observed spectra and those for the E′ centre in glassy SiO2 are discussed.

Properties of hydrogenated and fluorinated amorphous silicon–carbon alloy films prepared by magnetron sputtering

Abstract Hydrogenated and fluorinated amorphous silicon-carbon alloy films have been prepared by magnetron sputtering of silicon in Ar–CH4–CF4 gas mixtures. The dependence of compositional, structural, optical and optoelectronic properties of the films on the ratio R H of the partial pressure of CH4 to the total gas pressure and the corresponding ratio R F for CF4 have been investigated. It is found that (i) the optical band gap as well as the activation energy of the dark conductivity is controllable, (ii) SiC bonds are formed easily and (iii) the photoconductivity is improved by about one order of magnitude, compared with the films prepared using Ar-H2-CF4 gas mixtures reported previously. In addition, several kinds of extrema against R H were observed in such quantities as the room-temperature photoconductivity, the edge-width factor B in the optical absorption spectrum, and the activation energy of the photoconductivity. In the films having these extrema, the AM1 photoconductivity and photosensitivity...

Effect of hydrogen on the properties of magnetron sputtering of hydrogenated amorphous silicon carbon alloy films

Hydrogenated amorphous silicon carbon alloy films have been prepared by magnetron sputtering of silicon in methane-hydrogen-argon gas mixtures, and the dependence of film properties on hydrogen partial pressure (PH) as well as methane partial pressure against total gas pressure has been investigated. With increasing PH, the concentration of carbon increases, accompanied with the increase in the number of Si–C bonds, in spite of the unchanging partial pressure of methane. Following this, the optical band gap and activation energies of dc conductivities increase, and the photoconductivity as well as the dark conductivity decreases. The intensity of Si–H bonds is almost unchanged, while that of C–H bonds increases. These results are discussed mainly from the standpoint of the change of deposition process composed of the chemical decomposition of methane and the physical sputtering of silicon.

Valence-electron properties of a-Si 1 − xC x:H studied by UPS and EELS

The experimental results of UPS and EELS studies on hydrogenated amorphous silicon-carbon alloy films are presented. The influence of doping and surface state on valence band spectra and the electronic structure of the alloy materials has been described.

Properties and Local Structure of Plasma-Deposited Amorphous Silicon-Carbon Alloys

ABSTRACTHydrogenated amorphous silicon-carbon alloy films were plasma-deposited from metnane and silane, varying gas ratio, R.F. power and substrate temperature. Carbon addition increases the optical gap, but also raises the dangling bond density while decreasing conductivity. Low C alloys can be gas-phase doped both p and n type. In the IR spectra the various Si-C stretching modes observed between 650 and 780 cm-1 are explained by back bonding variations. A tentative method of assigning this shift to back bonding of C to the Si is given. A distribution of modes is observed for all alloys, with each mode appearing even at 2% C. The distribution is sensitive to substrate temperature, but is stable after vacuum annealing to 400°C.

Influence of rf power on the properties of hydrogenated amorphous silicon carbon alloy films prepared by magnetron sputtering of silicon in methane-argon gas mixtures

The rf power dependence of structural, optical, electrical, and optoelectronic properties of hydrogenated amorphous silicon carbon alloy films prepared by magnetron sputtering of silicon in methane-argon gas mixtures has been investigated. With increasing rf power, the optical band gap and the activation energy of dark conductivity decrease, accompanied by a decrease in the concentration of Si-C bonds. The dark conductivity and the photoconductivity increase with increasing rf power. These results are discussed in terms of the compositional and structural change of the films with rf power, such as the factor of preferential attachment of hydrogen to carbon deduced from IR measurements, and the conduction-band tail width deduced from optical absorption spectra or from temperature dependence of photoconductivity.

Defects in hydrogenated amorphous silicon-carbon alloy films prepared by glow discharge decomposition and sputtering: A Morimoto et al, J Appl Phys, 53 (11), 1982, 7299–7305

Defects in hydrogenated amorphous silicon-carbon alloy films prepared by glow discharge decomposition and sputtering: A Morimoto et al, J Appl Phys, 53 (11), 1982, 7299–7305

Highly photoconductive and photosensitive hydrogenated amorphous silicon carbon alloy films prepared by magnetron sputtering

Undoped hydrogenated amorphous silicon carbon alloy thin films were prepared by the magnetron sputtering of silicon in a gas mixture of methane argon. It is found that the photoconductivities of the films with carbon concentration above 15% are one order of magnitude or more larger than the films prepared by the glow discharge decomposition of silane-methane gas mixture reported by other groups before now. Moreover, the photosensitivities of these films are larger than those of the glow discharge films, as a result of small dark conductivities of the former compared with those of the latter.

Temperature-Independent Photoluminescence in Amorphous Si1-xCx: (F, H) Films with Low Defect Density

Photoluminescence and electron spin resonance measurements were carried out on amorphous silicon-carbon alloy film containing both F and H (a-Si1-xCx: (F, H)) prepared by the glow discharge decomposition of a mixture of SiH4 and CF4 gas. The a-Si1-xCx:(F, H) film, which had a wide optical gap (about 2.8 eV) had a smaller spin density and a photoluminescence with a higher intensity at room temperature and with a weaker temperature dependence than the a-Si1-xCx:H film with a similar optical gap. The temperature-independent photoluminescence appears to be due to an increase in the width of the band tail caused by the incorporation of F atoms.

Defects in hydrogenated amorphous silicon-carbon alloy films prepared by glow discharge decomposition and sputtering

Properties of hydrogenated amorphous silicon-carbon alloy (a-Si1−xCx :H) films prepared by radio frequency (rf) glow discharge decomposition and rf sputtering have been investigated by means of electron spin resonance (ESR), infrared absorption, optical absorption, and photoconductivity measurements. Although the number of C-H per C atom [C-H]/[C] is larger than that of Si-H per Si atom [Si-H]/[Si], the ESR spin density increases greatly with the C content. The increase in the density of dangling bonds may be related to the fact that the number of H atoms in gathered phase increases with an increase in x. ESR measurements also give useful information about the preferential formation of C or Si dangling bonds and the atomic distribution of Si and C through a compositional dependence of the g value. A remarkable feature for a-Si1−xCx :H film is that the presence of C atoms in the amorphous network makes the Si-H bond in a-Si1−xCx :H more stable than that in a-Si:H.

Control of Optical Gap in a-SixC1-x: H Alloy Films Produced by Reactive Sputtering Method

Hydrogenated amorphous silicon-carbon alloy (a-SixC1-x: H) films are prepared by simultaneous if reactive sputtering of silicon and graphite in a H2–Ar gas mixture. The optical gap E0 of a-SixC1-x: H depends on alloy composition x and preparation conditions. The optical gap E0 of a-SixC1-x: H prepared under a same condition is ∼1.7 eV at x=1.0 (a-Si: H), increases with the decrease in x, reaches a maximum value of 2.2 eV at x=0.6 and then decreases with decrease in x, reaching ∼1.4 eV at x=0 (a-C: H). For films prepared at lower substrate temperature, the optical gap becomes larger. This behavior of the optical gap is discussed referring to the results of X-ray photoemission spectroscopy, infrared absorption measurements, etc., on a-SixC1-x: H.