Effects of HWCVD-deposited Seed Layers on Hydrogenated Microcrystalline Silicon Films on Glass Substrates
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0910-A08-05
Effects of HWCVD-deposited Seed Layers on Hydrogenated Microcrystalline Silicon Films on Glass Substrates Michael M. Adachi1, Wing Fai Lydia Tse1, Garnet Cluff2, Karen L. Kavanagh2, and Karim S. Karim1 1 School of Engineering Science, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada 2 Department of Physics, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada
ABSTRACT Microcrystalline silicon (µc-Si:H) was deposited by hot-wire chemical vapor deposition (HWCVD) using a graphite filament on glass substrates with and without a thin 50 nm µc-Si:H seed layer. Increasing silane concentration diluted in H2 led to a decrease in crystalline fraction as well in a decrease in dark conductivity and photo-conductivity. In addition, films deposited with a seed layer were found to have higher dark conductivity and photo-conductivity than those without a seed layer but deposited at slower growth rates. However, Raman spectroscopy showed that use of a seed layer resulted in only a small increase in crystalline fraction at the surface of the films which had thicknesses between 250-400nm. TEM measurements confirmed the crystalline nature of deposited films showing average grain sizes of 25 nm. INTRODUCTION Microcrystalline silicon deposited by the hot-wire chemical vapor deposition (HWCVD) technique has gained considerable attention in recent years due to the potential for fabricating more efficient and stable solar cells at higher deposition rates than conventional PECVD. In this study, HWCVD grown µc-Si:H seed layers have been grown using a graphite catalyzer filament with the aim of improving the nucleation and ultimately the electrical characteristics of µc-Si:H films grown on glass substrates. The growth of microcrystalline silicon by HWCVD using a graphite filament has been reported by Brühne et al. [1] and Bhusari et al. [2]. In particular, the advantage of the use of a graphite filament is that it has a higher stability and usable lifetime [3] compared to commonly used Ta and W filaments, leading to more reproducible results. EXPERIMENTAL Amorphous (a-Si) and microcrystalline silicon films were deposited in a commercially available HWCVD chamber capable of depositions on 4”×4” substrates. A single straight 10 cm graphite filament was used as the heated catalyzer. Filament temperatures were kept between 1500 and 1550 °C, measured using an optical pyrometer. The substrate to filament distance was kept at a constant value of df-s= 4 cm and total gas flow rate was held to a constant value of 300 sccm. Silane concentrations diluted in hydrogen gas were calculated as SC = [SiH4]/([SiH4]+[H2]) and ranged from 0.2% to 1%. Deposition pressure was 300 mTorr, set
using an automatically controlled throttle valve and the system base pressure was 5x10-9 Torr. Films were deposited on 3.3 cm x 3.3 cm Corning 1737 glass substrates for electrical conductivity and Raman measurements and on a sacrificial SiNx coated silicon wafer for Transmission Electron Microscopy (TEM) measur
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