Studies of the mechanism of the decomposition of hydrogenated a-Si films

Abstract

The dehydrogenation of glow-discharge deposited a-Si films has been studied by in situ infrared spectroscopy in order to resolve the apparent inconsistency between the interpretation of previous manometric data and the assignments of the infra-red spectral features in these films. Our studies show that, on heating at about 350°C, there is no preferential reduction in the integrated band intensities near 2090 cm⁻¹, assigned to =SiH₂ stretching modes, relative to the band near 2000 cm⁻¹ assigned to the ≡SiH stretching mode. Accepting both infrared assignments our data conflicts with previous proposals that the low temperature dehydrogenation mechanism involves ≡SiH₂ groups alone. It appears that the low temperature dehydrogenation proceeds via the molecular elimination of hydrogen from regions in the film where bound hydrogen atoms are in close proximity. These hydrogen atoms may be incorporated either as monohydride or dihydride groups. The model, therefore, allows a consistent interpretation of the manometric and infrared data to be made without the need to question the assignment of the 2090 cm⁻¹ band.