Low Substrate Temperature Deposition of Crystalline SiC using HWCVD
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A10.6.1
Low Substrate Temperature Deposition of Crystalline SiC using HWCVD S. Klein, R. Carius, L. Houben1, F. Finger Institut für Photovoltaik, Forschungszentrum Jülich, 52425 Jülich, Germany Tel: +49-2461-61-2813, Fax:+49-2461-61-3735, email: [email protected] 1 Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany
ABSTRACT Microcrystalline silicon carbide (µc-SiC) was prepared at substrate temperatures between 300°C and 450°C using Hot Wire Chemical Vapour Deposition (HWCVD). The SiC films were deposited from monomethylsilane (MMS) diluted in hydrogen on glass and crystalline silicon substrates. The influence of the hydrogen dilution on the deposition rate and the structural and the optoelectronic properties was investigated. Infrared and Raman spectroscopy and transmission electron microscopy (TEM) were applied to study the structural properties. Highly crystalline material with large columnar grains was obtained at high hydrogen dilutions. The optical absorption below the band gap is high and the dark conductivities are far above the values expected for intrinsic SiC. At lower hydrogen dilution, less crystalline or amorphous Si1-xCx is growing, showing broader IR- and Raman peaks, lower dark conductivity and higher absorption above the band gap energy. An extended nucleation zone with large structural disorder was observed even for highly crystalline material. INTRODUCTION Crystalline silicon carbide (SiC) has a number of unique properties, i.e. a large band gap and a high carrier mobility, which make the material an excellent candidate for various optoelectronic devices, including blue LEDs and high speed, high power or high temperature electronic devices. The large optical band gap of SiC makes the material suitable also as window layers in solar cells and may even replace TCO materials. High quality SiC is so far prepared at high substrate temperatures, i.e. above 1000 °C, but material growth at lower temperatures has been a target for many years. Reasonable epitaxial growth has been achieved at temperatures of about 700 °C [1], but this temperature is still too high for applications as in thin film solar cells on cheap glass substrates. In the 80's Hattori et al [2] reported the preparation of highly conductive µc-SiC:H films for optoelectronic and photovoltaic applications. Raman spectra revealed that the material was a mixture of µc-SiC:H, µcSi:H and a-Si1-xCx:H. Recently, the deposition of µc-SiC:H at substrate temperatures below 600°C was reported by several groups [3-6] using PECVD, sputtering, and also HWCVD. The present study investigates the preparation of SiC-films at low substrate temperatures using hot-wire chemical vapour deposition (HWCVD) and monomethylsilane as deposition gas. The influence of the deposition parameters, in particular the hydrogen dilution, on the structural and electronic properties and the structural evolution is investigated. EXPERIMENTAL DETAILS SiC films were prepared by HWCVD in an ultra-high vacuum multi-chamber deposition system desig
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