Deposition of hydrogenated amorphous silicon (a-Si : H) films by hot-wire chemical vapor deposition (HW-CVD) method: Role of substrate temperature

摘要

Hydrogenated amorphous silicon (a-Si:H) thin films were deposited from pure silane (SiH4) using hot-wire chemical vapor deposition (HW-CVD) method. We have investigated the effect of substrate temperature on the structural, optical and electrical properties of these films. Deposition rates up to 15 angstrom s(-1) and photosensitivity similar to 10(6) were achieved for device quality material. Raman spectroscopic analysis showed the increase of Rayleigh scattering in the films with increase in substrate temperature. The full width at half maximum of TO peak (Gamma(TO)) and deviation in bond angle (Delta theta) are found smaller than those obtained for P-CVD deposited a-Si:H films. The hydrogen content in the films was found < 1 at% over the range of substrate temperature studied. However, the Tauc's optical band gap remains as high as 1.70 eV or much higher. The presence of microvoids in the films may be responsible for high value of band gap at low hydrogen content. A correlation between electrical and structural properties has been found. Finally, the photoconductivity degradation of optimized a-Si:H film under intense sunlight was also studied. (c) 2007 Elsevier B.V. All rights reserved.