The electrical and optical properties of hydrogenated amorphous silicon, prepared by R.F. sputtering in Ar/$H_2$ mixture with various hydrogen partial pressure ($P_H$), have been investigated. All the samples were prepared at a fixed power(300W) and substrate temperature(200℃), and the thickness ranged between 1.0 and 1.5㎛ . The film properties were characterized by measuring the dark conductivity, optical band gap, and infrared vibrational absorption. The hydrogen could be incoporated into silicon matrix in concentrations from 5% to 27% (in atomic percent) by increasing the hydrogen partial pressure.
For the low $P_H$(<2 mTorr), the localized states in the gap were reduced, and activation energy of conductivity and the optical band gap increased with $P_H$ due to the compensation of dangling bonds and other defects by H.
For the high $P_H$(>2 mTorr), activation energy and optical band gap were increased slowly, conductivity decreased as $P_H$ is increased, even when the hydrogen content saturated and decreased. These results may be interpreted in terms of the decreasing of carrier mobility and change of the DOS near the band edge due to the increasing of dihydride bonds relative to the monohydride bonds with $P_H$, instead of the compensation of dangling bond by H.
