AMORPHOUS AND MICROCRYSTALLINE SILICON FILMS OBTAINED BY HOT-WIRE CHEMICAL-VAPOR-DEPOSITION USING HIGH FILAMENT TEMPERATURES BETWEEN 1900 AND 2500-DEGREES-C

The effects of hydrogen dilution and substrate temperature on the opti cal, transport and structural properties of silicon thin films deposit ed by hot-wire chemical vapour deposition using filament temperatures between 1900 and 2500 degrees C are reported. Amorphous silicon films with a Tauc bandgap of 1.65 eV, a photoconductivity-to-dark-conductivi ty ratio above 10(5), a deep defect density of 10(16) cm(-3), an Urbac h energy of 55 meV and a structure factor R approximate to 0.2 were pr epared with deposition rates up to 40 Angstrom s(-1) for hydrogen dilu tions below 80%. The best properties were obtained for undiluted films deposited at a substrate temperature of 220 degrees C. For hydrogen d ilutions above 80%, microcrystalline films were obtained with low grow th rates (below 3 Angstrom s(-1)) for all substrate temperatures studi ed (between 100 and 400 degrees C) regardless of the filament temperat ure. The Raman spectra show a high crystalline fraction and a small gr ain size. In this filament temperature regime, the growth mechanism an d film properties are controlled by the high flux of atomic hydrogen.