Influence of argon dilution on the growth of amorphous to ultra nanocrystalline silicon films using VHF PECVD process

Abstract

• Silicon films were grown by variation in argon concentration ( f ar %). • Nucleation and growth of crystallites were observed at f ar = 82% and 87%, respectively. • Amorphous films showed photosensitivity of five orders of magnitude. • FTIR showed changes in the hydrogen bonding configuration with variation in f ar %. Hydrogenated Silicon (Si:H) thin films were deposited by very high frequency plasma enhanced chemical vapor deposition (VHF PECVD) technique from silane (SiH 4 ) diluted in various argon (Ar) concentration ( f ar ). The effect of argon concentration (53–95%) on the growth and properties of Si:H films was investigated. Device quality amorphous silicon films were grown at f ar = 53% and 63% showed photosensitivity of five orders of magnitude. Nucleation of crystallites were started at f ar = 82% whereas mixed-phase of amorphous (a-Si:H) and ultra nanocrystalline silicon thin film (ultra nc-Si:H) was grown at 87% of f ar . The nucleation and growth of crystallites were clearly observed in the AFM images. Raman spectra showed the splitting and blue shift of TO mode for the films grown at f ar = 82% and 87%, respectively. The variation in the hydrogen bonding configuration of these Si:H films were observed by FTIR measurement. The difference in the temperature dependent dark conductivity during heating and cooling runs decreases as the fraction of clustered Si–H bond increases in the films.