Morphology and micro-structural studies of distinct silicon thin films deposited using very high frequency plasma enhanced chemical vapor deposition process

In the present investigation three distinct silicon thin films designated as (i) amorphous silicon, a-Si:H (ii) mixed structure consisting of small crystallites of silicon embedded in amorphous matrix, a-Si:H/nc-Si:H & (iii) mixed structure of larger crystallites embedded in amorphous matrix, a-Si:H/μc-Si:H has been chosen to perform the study of morphology, optical and electrical characteristics. These films were deposited using 60 MHz assisted VHF (very high frequency) plasma enhanced chemical vapor deposition (PECVD) process at different argon dilution (fAr) of 10%, 60% and 80%, respectively in silane gas. The micro-structure of these films was studied using Raman spectroscopy (RS), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Well arranged network of micro/nanocrystalline silicon films with well oriented crystallographic lattice planes have been obtained at high argon dilution. The average grain size estimated using Raman spectroscopy was about 2-4 nm. HRTEM confirms the existence of small and large sized crystallites embedded in amorphous matrix. FESEM and AFM microscopy exhibits the change in morphology from amorphous to varied size crystallites in amorphous silicon matrix with increasing argon dilution. The electrical and optical properties are well correlated with the amorphous and crystalline distribution in these silicon films.