Device-quality wide-gap hydrogenated amorphous silicon films deposited by plasma chemical vapor deposition at low substrate temperatures.

Hydrogenated amorphous silicon (a-Si:H) films have been fabricated by a plasma chemical vapor deposition (plasma-CVD) method at low substrate temperatures (Ts : 80 or 50 °C) to obtain wide-gap films. Device-quality wide-gap films (photoconductivity under AM-1.5, 100 mW/cm2 illumination ∼10−5 Ω−1 cm−1, ratio of photoconductivity and dark conductivity ∼106, and Tanc’s gap ∼2 eV) are obtained at low Ts, by optimizing the plasma parameters or by diluting the material gas (SiH4) with H2. Experimental results suggest that lowering the deposition rate of a-Si:H films is an important factor in obtaining high-quality films at low Ts using a plasma-CVD method.