Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD

We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap

PECVD Amorphous Silicon Nitride at 120°C for a-Si:H TFTs.

AbstractThe effect of a-SiNx films stoichiometry and their physical properties on the electrical integrity and masking ability is studied. The films are deposited at 120° C by 13.56 MHz PECVD from SiH4+NH3 + N2 gas mixture. They have the N/Si ratio of 1.4 to 1.7 and hydrogen concentration of 25 to 40 at.%. The electrical characterization was carried out by I-V measurements. An electrical resistivity of ∼1016 Ohm-cm and breakdown voltage of 5.5 MV/cm have been achieved for our PECVD nitride films. The performance of a-Si:H TFTs with these silicon nitride as the gate dielectric and passivation layer has been also evaluated.</jats:p

The Valence Band Tail Density of States and Bond Angle Distortion in a-SiN_x: H Alloys

AbstractFilms of a-SiNx:H with x = 0.0..0.62 were deposited by glow discharge decomposition of (10% SiH4+90%/H2 )+ NH3 mixture. The chemical bonding and composition of films were investigated with using of infrared spectroscopy. The deformation energy per Si atom connected to bond bending Vkθ was calculated from data of Raman scattering. Characteristic energy of valence band tail (VBT) states distribution, E0v, were determined fromrsubgap absorption spectra. The dependencies of E0v and Vkθ on film composition, x, were considered in order to estimate the influence of the bond angle disorder on the distribution of VBT states.The essential difference in behavior of E0v and Vkθ dependencies on x was found for Si-rich (x&lt;0. 15) alloys. When Vkθ value increase with x, the E0v parameter stays almost constant; while at x&gt;0. 15 the E0v increase with x as well as the VKO. It means that bond angle disorder in the bulk of the material contributes to VBT characteristic energy, but it is not the only source. Another factors as it was shown may be connected with valence states of Si atoms, localized near inner boundaries.</jats:p