Study of Infra-red Spectroscopy on Bonding Environment and Structural Properties of Nanocrystalline Silicon Thin Films Grown by VHF-PECVD Process

Infra-red spectroscopy as an effective tool used to establish platelet like configuration in nanocrystalline silicon thin films (nc-Si:H). These films were deposited using 60 MHz assisted very high frequency plasma enhanced chemical vapor deposition process with varying pressure from 4 to 40 Pa. The deposited films were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), Raman spectroscopy (RS), Fourier transform infra-red spectroscopy (FTIR), Dark conductivity, UV-Vis Spectra and photosensitivity. Infra-red studies of these films reveals that the hydrogen bonding is a platelet like configuration (Si-H groups at 2033 cm− 1) located at grain boundaries resulting in crystalline grains wrapped with hydrogen rich amorphous tissues that provides good passivation resulting in less dangling bonds on grain boundary surface. Structural transformation from amorphous silicon (a-Si:H) to nanocrystalline (nc-Si:H ) phase has been identified at pressure of 24 Pa. The increase in deposition pressure provides clear evidence of improved crystallinity (∼ 37%) which were depicted by increased grain size (∼ 12 nm), reduced hydrogen bonded content (∼ 5.0%), widening of optical gap (∼ 1.9 eV) with enhanced polymerization in the network.