Microcrystalline SiC Research Articles

Optoelectronic properties of highly conductive microcrystalline SiC produced by laser crystallisation of amorphous SiC

The optoelectronic properties of undoped and doped microcrystalline silicon carbide thin films, prepared by excimer (ArF) laser crystallisation of plasma enhanced chemical vapour deposited hydrogenated amorphous silicon carbide, are analysed. All films show more than six orders of magnitude increase relative to the conductivities before the laser crystallisation. It is shown that the increase in conductivity is not predominantly due to the activation of dopant atoms. However, dopant sites, but not carbon content (up to 30 at%), play an important role in electrical transport in μc-SiC. We also report the observation of blue photoluminescence at room temperature from the undoped laser irradiated samples having a carbon content of 35 at%. The spectrum exhibits two visible peaks (1.8 eV and 2.6 eV), while the as-deposited films show only the 1.8 eV peak.

Microcrystalline SiC Films Grown by Electron Cyclotron Resonance Chemical Vapor Deposition at Low Temperatures

The characteristics of microcrystalline silicon carbide (µ c-SiC) films deposited using an electron cyclotron resonance chemical vapor deposition system at low temperatures have been investigated. The effect of microwave (MW) power on the SiC crystallinity is studied. According to the results of Fourier transform infrared absorption spectra, plan-view transmission electron microscopy, and the plasmon loss peaks in X-ray photoelectron spectroscopy, Si-C bonds form when the MW power is above 500 W for deposition at 500° C. The SiC crystallinity improves monotonically with MW power. The amount of incorporated carbon atoms in the grown films increases with MW power up to the concentration of 50% at 1500 W. The dependence of the surface morphology and the mean roughness of the films on MW power is examined using the contact mode atomic force microscopy.

Diamond films grown on p-type microcrystalline-SiC:H/crystalline-Si substrates

In this work we have used a two-step process to prepare diamond thin films. A boron-doped microcrystalline SiC (p-type μc-SiC:H) buffer layer was first deposited onto smooth crystalline silicon (x-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD). Secondly, diamond polycrystalline films were grown by hot-filament CVD on the μ c-SiC:H x-Si substrates. The resulting films were characterized by Auger electron spectroscopy, electron energy loss spectroscopy, secondary electron microscopy and Raman spectroscopy. The effect of the substrate preparation on the nucleation and growth of diamond films on μ c-SiC:H x-Si substrates is discussed in terms of the presence of Si and SiC microcrystalline clusters embedded in the amorphous network structure of the μc-SiC:H films.

Improved Amorphous Silicon Solar Cells Using RPCVD

We have studied the depositions of amorphous silicon, silicon carbon alloy, doped microcrystalline silicon in order to apply these films as the component materials for the p-i-n and double stacked solar cells. We have obtained low band gap a-Si:H by decreasing the deposition rate under the proper preparation conditions and highly conductive, thin microcrystalline Si and SiC layers. We have developed a stable a-Si/a-Si double stacked solar cell with a conversion efficiency of ∼ % using narrow band gap a-Si:H as a i-layer of bottom cell.The performance of this cell does not degrade until 100 hrs illumination under 350 mW/cm2.

Influence of doping on the structural and optoelectronic properties of amorphous and microcrystalline silicon carbide

Amorphous and microcrystalline silicon carbide, undoped and doped, has attracted a great attention for its optical and electrical properties. The introduction of dopant atoms in the network of amorphous films permits the control of electrical properties but it gives rise to a decreasing of the optical gap. Microcrystalline SiC:H films seem to provide films having a wide range of electrical conductivities without drastic change in the optical gap. This paper presents the results of a detailed study on the effects of boron and phosphorus doping on structural, optical, and electrical properties of a-SiC:H and μc-SiC:H films. An optical gap as high as 2.1 eV, together with a conductivity of 10−3 Ω−1 cm−1, are shown by doped μc-SiC:H.

Microcrystallization formation in silicon carbide thin films

Abstract In the present work, two different methods of promoting microcrystal formation in the amorphous network of hydrogenated silicon carbide (Sic: H) have been investigated: glow-discharge plasma-enhanced chemical vapour deposition (PECVD) with high hydrogen dilution and high power density, and annealing of device-quality amorphous SiC: H films. The microcrystalline SiC: H films directly produced by PECVD have a high electrical conductivity (10−5ω-1cm−1), a large energy gap (2–2.1eV) and they are hydrogenated. The annealed films have a high electrical conductivity (7× 10−4ω−1cm−1) and a smaller optical bandgap and they do not contain hydrogen.

Amorphous and Microcrystalline SiC as New Synthetic Wide Gap Semiconductors

ABSTRACTA review is given on recent progress in amorphous and microcrystalline silicon-carbide (a-SiC, nc-SiC) semiconductors and their technological applications to optoelectronic functional devices. Firstly, some significant properties in this alloy as a new synthetic material are pointed out with recent advances of thin film technologies, such as plasma CVD, ECR-CVD and ion-beam CVD etc. There exists an energy gap controllability from 1.7eV to 3.6 eV with retaining the valency electron control from n-type through i- to p-type semiconductors. While its conductivity can also be controlled more than ten order of magnitudes, e.g., from 10-9to 102 Scm-1 by controlling the impurity doping and preparation conditions.Secondly, a series of technical data on the electronic and optoelectronic properties of a-Si, C1−x C1−x and μ-SiC are demonstrated from recent achievements. In the final part of the paper, current state of the art in the field of optoelectronic applications from live technologies on amorphous silicon solar cells. a-SiC visible light LED and EL devices are reviewed. A technological evolution from “microelectronics” to “macroelectronlcs” will be discussed.

Spectroscopic studies of the structure of amorphous and microcrystalline SiC prepared by the polymer route

The structural evolution of amorphous and microcrystalline SiC prepared from polycarbosilane was studied using various spectroscopic methods, 13C CPMAS NMR (cross-polarization, magic angle spinning nuclear magnetic resonance), ESR (electron spin resonance), FTIR (Fourier transformation infrared spectroscopy), and Raman. These studies indicate that the carbon-rich a-SiC has two major structural defects, C==C double bonds and C-dangling bonds. Both defect concentrations vary with firing conditions. The effect of hydrogen on the defect concentrations was also investigated by heat-treating the sample under hydrogen atmosphere. The mechanisms of the conversion process were discussed and the structural models for both amorphous and microcrystalline SiC were also proposed.

Toward 20% Efficiency With a-Si // poly-Si Tandem Solar Cell

ABSTRACTA series of experimental investigations has been made on the a-Si // poly-Si tandem solar cell which is one of the most promised candidate of high cost-performance photovoltaic cell, e.g., high efficiency, low cost with almost no light induced degradation. Employing high conductivity with wide optical band gap p type microcrystalline SiC (μ-SiC) as a window material together with a-SiC as an interface buffer layer and also n type μc-Si as a back ohmic contact layer in the poly-Si based bottom cell, the conversion efficiency of 17.2 % has been obtained. Combining an optically transparent a-Si p-i-n cell as a top cell with an optical coupler between the top and the poly-Si bottom cell, a total efficiency of 20.3 % has been obtained so far on the four-terminal stacked mode structure. A systematic technical data for the optimization of cell structure variation on the developed tandem solar cells are presented and further possibility to improving the performance are discussed.

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

ABSTRACTExperimental 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.

Nmr and Esr Studies of the Structural Defects of Amorphous and Microcrystalline Sic Prepared by the Polymer Route

ABSTRACTAmorphous SiC was prepared by firing the polycarbosilane to various temperatures ranging from 500°C to 1200°C. However the l3c CPMAS NMR and ESR studies show that the carbon rich SiC has two major structural defects, C=C bonds and C-dangling bonds. Both defects concentrations vary with different sample firing conditions. Hydrogen has dramatic effect on decreasing the defect concentrations when used in the sample firing.

Doped Amorphous SiC, Mixed Carbide and Oxycarbide Thin Films by a Liquid Route

ABSTRACTA new family of disordered materials called amorphous covalent ceramics (ACC) has been obtained by pyrolysis of metal-organic polymers. The transformation from polycarbosilane to amorphous and microcrystalline SiC has been studied. New a-SiC:H thin films have also been prepared by the polymer solution. Electrical and optical properties of this new a-SiC have studied. Amorphous binary carbide and oxycarbide have also been prepared by crosslinking polycarbosilane and metal alkoxides. The p-n control of this new a-SiC:H has been achieved, which also lead to the possible device applications.

The Effect of Hydrogen on the Structure of Amorphous and Microcrystalline Sic Prepared by the Polymer Route

AbstractAmorphous SiC:H thin films have been deposited on different substrates using metal-organic polymer solutions. The structure of the amorphous phase has been proposed as the rings of Si and C atoms with various sizes. Microcrystalline phase can be produced when fired at temperatures higher than 1000°C. 13C MAS-NMR shows the evidence of the C=C-double bonds. ESR results show the major defects in this material are C-dangling bonds. As predict, defects can be decreased by heat treatment in H2 atmosphere.

Optoelectronics and Photovoltaic Applications of Microcrystalline Sic

AbstractA review is given of the electrical and optical properties of hydrogenated microcrystalline silicon carbide (μc-SiC:H) films prepared by ECR (Electron Cyclotron Resonance) plasma chemical vapor deposition. The material produced with the ECR plasma technology has a very wide energy gap from 2 to 2.8 eV with good valency electron controllability, e.g., a dark conductivity as high as 10 Scmg− which is more than seven orders of magnitude larger than that of amorphous SiC:H.Employing this material as a wide gap heterojunction window, 15.4% and 12.0% conversion efficiencies have been achieved with the structures of ITO/p type μc-SiC:H/n type poly-Si and p type vc-SiC:H/i type a-Si:H/n type Pc-Si:H heterojunction solar cells, respectively. The successful development of a visible light thin film light emitting diode show the promise of microcrystalline materials for optoelectronic applications.

Highly conductive p-type microcrystalline SiC:H prepared by ECR plasma CVD

Highly conductive p-type microcrystalline SiC:H films have been prepared by ECR (electron cyclotron resonance) plasma CVD. The material with an optical energy gap of 2.25 eV exhibits a dark conductivity as high as 10 S cm -1 which is more than seven orders of magnitude higher than that of amorphous SiC:H prepared by conventional RF plasma CVD. The optimal energy gap can be controlled in the range from 2.0 to 2.8 eV, while retaining excellent conductivity. Utilizing this material as a wide-gap heterojunction contact in amorphous silicon solar cell, a conversion efficiency of 12.0% has been obtained with a large open circuit voltage.

Effects of neutron irradiation on fine structure and strength of sic fibers

Two types of SiC fibers, amorphous SiC(1000) (heat-treated at 1000°C) and microcrystalline SiC(1300) (heat-treated at 1300°C), were neutron-irradiated at 423 K to 8 × 10 23 and 2 × 10 24 n/m 2 , and at 923 K to 9 × 10 24 n/m 2 in JMTR ( E > 1 MeV). In the 423 K irradiation, density increased and X-ray radial distribution function (RDF) indicated that the atomic arrangement of SiC(1000) scarcely changed and that of SiC(1300) was disordered. Tensile strength and Young's modulus gradually increased with neutron fluences. In the 923 K irradiation, density increased and RDF indicated that the atomic arrangement of SiC(1300) scarcely changed and that of SiC(1000) was ordered. Young's moduli of SiC(1000) and SiC(1300) greatly increased. There were differences in density, tensile strength and Young's modulus between SiC(1000) and SiC(1300) before the irradiation, but their values became almost the same by the irradiation at 423 K to 2 × 10 24 n/m 2 and 923 K to 9 × 10 24 n/m 2 , respectively.

Valency control of P-type a-SiC:H having the optical band gap more than 2.5 eV by electron-cyclotron resonance CVD (ECR CVD)

Electron Cyclotron Resonance plasma CVD (ECR CVD) has been used to prepare highly conductive and wide band gap a-SiC:H of p-type conduction. A conductivity higher than 10 −1 Scm −1 has been obtained with an activation energy as small as 0.05 eV for p-type a-SiC:H having the band gap in the range from 2.0 eV to 2.9 eV. The high conductivity is found to be due to the formations of microcrystalline Si and SiC.

Raman study of SiC fibres made from polycarbosilane

We have examined the evolution of Raman spectra of SiC fibres through structural and compositional transformations caused by heat treatment. The SiC fibre was made from polycarbosilane. Raman spectra of the SiC fibre indicate that it consists of (i) amorphous or microcrystalline SiC, (ii) carbon microcrystals, and (iii) silicon oxide. The amount of microcrystalline carbon in the fibre increases with heat treatment temperature up to 1400° C, and it decreases abruptly in those fibres heat treated above 1500° C. The tensile strength of the fibre drops virtually to zero after the heat treatment at 1500° C. Carbon microcrystals are precipitated from the Si-C random network with excess carbon, and they are distributed uniformly in the fibre. These carbon particles suppress the growth of SiC crystals. It is shown that the carbon microcrystals play an important role in maintaining the high mechanical strength of the SiC fibre.