Structural interpretation of the vibrational spectra of a-Si: H alloys

The ir and Raman spectra of a-Si: H alloys produced by plasma decomposition of SiH4 are studied for a wide range of deposition conditions. The vibrational spectra display modes which can be characterized as predominantly hydrogen motions. Analysis of these modes shows four types of local Si-H bonding environments which are identified as SiH, SiH2, SiH3, and coupled SiH2 or (SiH2)n units. On the basis of these identifications, it is found that samples produced on high-temperature (above 200°C) substrates have SiH, SiH2, and (SiH2)n groups with very little SiH3. In contrast, the ir and Raman spectra of samples produced on room-temperature or cooled substrates are dominated by vibrational modes of SiH3 and (SiH2)n. The relative concentrations of these hydrogen-containing groups are not simply proportional to the total hydrogen concentration in a given sample.