Deposition of hydrogenated amorphous silicon (a-Si:H) films by hot wire chemical vapor deposition:: role of filament temperature

Hydrogenated amorphous silicon (a-Si:H) films were deposited using pure saline (SiH4) without hydrogen dilution by the hot wire chemical vapor deposition (HW-CVD) technique. The electrical, optical and structural properties of these films are systematically studied as a function of filament temperature (T-fil). The device quality a-Si:H films which were obtained at high deposition rate (3less than or equal tor(d)less than or equal to85 Angstrom/s) using filament temperature (1400less than or equal toT(fil)less than or equal to1900 degreesC) without hydrogen dilution show good structural, optical and electrical properties. However, the films deposited at higher filament temperature show an amorphous-to-microcrystalline transition. The FTIR spectroscopic analysis showed that a-Si:H films deposited at low filament temperature contain hydrogen mainly in mono-hydride (Si-H) configuration whereas films deposited at higher filament temperature have hydrogen in di-hydride (Si-H-2) or poly-hydride (SiH2)(n) complexes. The low hydrogen content (C-H) in the films indicates that the growth of a-Si:H films is mainly from the atomic species (Si and H) evaporated from the hot filament and hydrogen is incorporated in the film via gas phase reactions and substrate-gas interactions. The band gap, however, was found to be similar to1.71 eV or much higher. We suggest high band gap at low hydrogen content may be due to the presence of microvoids. Raman spectroscopic analysis showed the increase in structural disorder and Rayleigh scattering with increase in filament temperature. (C) 2003 Elsevier Science B.V. All rights reserved.