Structure and Optoelectronic Properties as a Function of Hydrogen Dilution of Micro-Crystalline Silicon Films Prepared b
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of Physics & Astronomy, University of North Carolina at Chapel Hill, Chapel Hill,
NC 27599-3255, USA. **National Renewable Energy Laboratory, Golden, CO 80401, USA. ABSTRACT Films prepared by hot wire CVD using H dilution ratio, R=H 2/SiH 4 , from 1 to 20 were studied by X-ray, Raman, PL, and conductivity measurements. We found that (a) when the dilution ratio reached R=3, the structure transition from amorphous to microcrystalline growth occured; meanwhile, PL spectrum showed a dual-peak at 1.3 and 1.0 eV; (b) the total intensity, band width, and peak position of the low energy PL band decreased with increasing H dilution; (c) both the Raman and PL measured from the transparent substrate side showed that initial growth tends to be amorphous and a portion of jic-Si was formed when R > 5; and (d) the conductivity activation energy first decreased from 0.68 to 0.15 eV when the film transition from a- to ýtc-Si; then increased slightly with increasing [ic-Si fraction. The results demonstrate that the variation of the H-dilution ratio has significant effects on both the film structures and the optoelectric properties. INSTRUCTION Microcrystalline silicon (ltc-Si:H) has been used in thin-film device technology, such as contact materials in MOS devices or as an active layer in thin film transistors (TFTs). Many methods have been used to grow the [tc-Si[1, 2]. However, a one-step low temperature and high growing rate process is desirable for device applications. The hot wire chemical vapor deposition (HWCVD) can achieve high growth rate with reasonable material quality. In this method, [tc-Si can be formed by varying growth parameters, such as the filament temperature (Tfil), gas pressure (P), substrate temperature (Ts), and H dilution ratio (R=H 2 /SiH
4
) [3-6]. When one has a
proper filament and substrate temperature, H-dilution is expected to be a simple and promising method for producing high quality lic-Si film. However, the effect of H dilution on the film microstructure is somewhat in contradiction. Brogueira et al. [3] reported that [ic-Si:H growth was achieved without H dilution at Tfil =1500 'C, Ts=220 'C, and P •
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