Structural and optical properties of a-Si:H/nc-Si:H thin films grown from Ar–H 2–SiH 4 mixture by plasma-enhanced chemical vapor deposition

Abstract

The structural and optical properties of hydrogenated amorphous silicon (a-Si:H)/nanocrystalline silicon (nc-Si:H) thin films, grown from high argon/hydrogen diluted silane by plasma-enhanced chemical vapor deposition (PE-CVD) using high rf power, were investigated. The growth rate decreased with increasing hydrogen flow rate and decreasing rf power, and increased slightly with increasing substrate temperature. For all samples deposited without hydrogen addition, SiH stretching was predominant as detected by infrared spectroscopy, whereas with hydrogen addition, the SiH intensity became lower than that of SiH 2 stretching. Moreover, the hydrogen content was found to decrease with increasing hydrogen flow rate and substrate temperature. Raman scattering clearly showed the nanocrystallites formed in the amorphous silicon matrix in the thin films deposited with hydrogen addition, and these films had higher optical band gaps. There was no direct relation between the hydrogen content and the optical band gap or edge width parameter due to the heterogeneity of the grown thin films. However, IR and Raman scattering spectra were found to be closely related to the microstructure of the grown thin films, and may provide clear information on the quality or heterogeneity of the films deposited using high rf power and high argon/hydrogen dilution. In addition, the smooth surface morphology and adherent stable structure of the grown thin films make them suitable for application in electronic devices.