Silicon–germanium films prepared from SiH4 and GeF4 by low frequency plasma deposition

The properties of silicon–germanium films (a-Si1−xGex:H,F) deposited by low frequency plasma enhanced chemical vapor deposition (LF PECVD) from SiH4 and GeF4 have been studied. The films were deposited in capacitive discharge at frequency f=110 kHz, substrate temperature Ts=300 °C, pressure P=0.6 Torr and power W=350 W. Ge gas mixture composition, Xg, determined as [GeF4]/[SiH4 + GeH4] was varied from Xg=0.1 to 1. The films were deposited from (1−Xg) SiH4 + XgGeF4 mixture without dilution, with Ar and with H2 dilution. Composition of the films was characterized by SIMS. The chemical bonding structure was studied by IR spectroscopy. It was found that the modes of Si–H, Ge–H, Si–Ge bonding depended on Ge content and gas dilutor. Transport of carriers was studied by the measurement of conductivity dependence on temperature. The reduction of activation energy from 0.86 to 0.39 eV and the increase of room temperature conductivity from 1 × 10−9 to 2.1 × 10−4 Ω−1 cm−1 were observed with the changes of Ge gas mixture Xg, from 0 to 1. No correlation between pre-exponent factor of conductivity σ0 and activation energy Ea was observed in the samples studied, in contrast to that in amorphous silicon (Meyer–Neldel rule). The data obtained are discussed in comparison with information available in literature on similar films obtained by alternative techniques.