Amorphous silicon

About: Amorphous silicon is a research topic. Over the lifetime, 26777 publications have been published within this topic receiving 423234 citations.

Influences of a high excitation frequency (70 MHz) in the glow discharge technique on the process plasma and the properties of hydrogenated amorphous silicon

Abstract: Hydrogenated amorphous silicon has been prepared at a plasma excitation frequency in the very-high-frequency band at 70 MHz with the glow discharge technique at substrate temperatures between 280 and 50-degrees-C. The structural properties have been studied using hydrogen evolution, elastic recoil detection analysis, and infrared spectroscopy. The films were further characterized by dark and photoconductivity and by photothermal deflection spectroscopy. With respect to films prepared at the conventional frequency of 13.56 MHz considerable differences concerning the electronic and structural properties are observed as the substrate temperature is decreased from 280 to 50-degrees-C. Down to a substrate temperature of 150-degrees-C the electronic film properties change only a little and the total hydrogen content c(H) and the degree of microstructure that can be directly correlated to c(H) increase only moderately. Below 150-degrees-C the electronic properties deteriorate in the usual manner but still the total hydrogen content does not exceed 21 at.% even at a substrate temperature of 50-degrees-C. It is argued that the influence of the higher excitation frequency on the plasma and on the growth kinetics plays a key role in this context by allowing a highly effective dissociation of the process gas with the maximum ion energies remaining at low levels. It is concluded that deposition processes at higher excitation frequencies can have important technological implications by allowing a decrease of the deposition temperature without losses in the material quality.

Room temperature reactions involving silicon dangling bond centers and molecular hydrogen in amorphous SiO2 thin films on silicon

Abstract: Exposing thin films of amorphous SiO2 to molecular hydrogen at room temperature converts some silicon dangling bond defects, E’ centers, into two hydrogen coupled complexes These reactions may play important roles in radiation and hot carrier instabilities in metal/oxide/silicon devices

Determination of complex dielectric functions of ion implanted and implanted-annealed amorphous silicon by spectroscopic ellipsometry

Abstract: Measuring with a spectroscopic ellipsometer (SE) in the 1.8–4.5 eV photon energy region we determined the complex dielectric function (ϵ = ϵ1 + iϵ2) of different kinds of amorphous silicon prepared by self‐implantation and thermal relaxation (500 °C, 3 h). These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted a‐Si (i‐a‐Si) differs from that of relaxed (annealed) a‐Si (r‐a‐Si). Moreover, its ϵ differs from the ϵ of evaporated a‐Si (e‐a‐Si) found in the handbooks as ϵ for a‐Si. If we use this ϵ to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the Davis–Mott plot based on the relation: (ϵ2E2)1/3 ∼ (E− Eg). The results are: 0.85 eV (i‐a‐Si), 1.12 eV (e‐a‐Si), 1.30 eV (r‐a‐Si). We attribute the optical change to annihilation of point defects.

Top-Gate Staggered Amorphous Silicon Thin-Film Transistors: Series Resistance and Nitride Thickness Effects

Abstract: Top-gate staggered hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were fabricated over large-area glass substrates using a selective phosphorus-treatment (PT) of indium-tin-oxide (ITO) source/drain electrodes. The ohmic contact between a-Si:H and ITO had a specific contact resistivity of about 0.18 Ωcm2. For a 100-µm channel length TFT, the source/drain series resistance contributes less than 5% of the total drain-to-source resistance. This contribution increases to about 25% for a 10-µm channel length TFT. Our study also indicated that the interface quality of a-Si:H/a-SiNx:H is amorphous silicon nitride (a-SiNx:H) and a-Si:H thickness independent and dependent, respectively. Effective interface state densities of about 1.5×1012 cm-2eV-1 and 3.2×1012 cm-2eV-1 were obtained for top-gate TFTs with a 1300 and 300 A thick a-Si:H films, respectively. Channel conductance activation energy of about 0.1 eV was measured for this top-gate TFT with 300 A a-Si:H.

Chemical and physical sputtering of fluorinated silicon

Abstract: Molecular dynamics simulations were performed on low‐energy argon‐ion bombardment (200, 50, and 20 eV) of silicon layers with varying amounts of fluorine incorporated. At low fluorine incorporation in the layers (F/Si<0.5), only physical sputtering was observed, although the physical sputtering yield increased compared to pure amorphous silicon. At higher levels of fluorine incorporation into the silicon layer, ion impact resulted in the formation of weakly bound SiFx (x=1–3) species in the layer. This phenomenon appears to be similar to chemical sputtering as defined by Winters and Coburn [H. F. Winters and J. W. Coburn, Surf. Sci. Rep. 14, 164 (1992)]. The overall yield, due to both physical and chemical sputtering, was found to follow a square‐root dependence on ion energy. The threshold ion impact energy for the formation of weakly bound species in heavily fluorinated silicon layers extrapolated to ≤4 eV, and for physical sputtering to about 20 eV. The simulations imply that the source of the ion‐neut...