Effects Of Plasma Hydrogenation Research Articles

Plasma Hydrogenation of High-Carbon Structural Steel Wires under Different Prestressing Levels

High-carbon structural steel wires were prestressed to various levels in a plasma hydrogenation environment and then pulled in a slow strain rate test (SSRT). The effect of plasma hydrogenation under different prestressing levels on the material's tensile response and hydrogen embrittlement was noted. It was found that the ultimate tensile strength (UTS), yield strength, and ductility of the steel wire samples are decreased by plasma hydrogenation and prestressing levels. The more drastic decrease in the UTS, yield strength, and ductility is found in the plasma hydrogenated prestressing steel to a higher prestressing level. Moreover, the hydrogen embrittlement index of the steel wire samples is significantly increased by plasma hydrogenation and prestressing level. The highly plasma hydrogenated prestressing steel wire samples exhibit complete brittle fracture. A mixed mode of fracture, i.e., ductile and brittle, was observed at the surface of the plasma hydrogenated prestressing steel wire samples at lower levels. The hydrogen embrittlement areas at the fracture surfaces of steel wire samples are observed to increase with plasma hydrogenation and prestressing levels. More severe hydrogen cracking and blistering resulted in the fracture surfaces of plasma-hydrogenated prestressing steel wire samples with higher levels.

Effects of plasma hydrogenation on low temperature growth of nanocrystalline cubic SiC thin films

The effects of plasma hydrogenation on the fabrication of nanocrystalline cubic silicon carbide (SiC) thin films on Si (100) are investigated. Our results indicate that plasma hydrogenation is an effective method to reduce the deposition temperature and to improve the composition and microstructure of the cubic SiC (β-SiC) thin films. In particular, the crystal particle size and the oxygen diffusion can be controlled. The mechanism is discussed.

Effect of hydrogenation on the electrical and optical properties of CdZnTe substrates and HgCdTe epitaxial layers

In this paper, we report the experimental observations on the effect of plasma hydrogenation in passivating intrinsic point defects, shallow/deep levels and extended defects in low-resistivity undoped CdZnTe crystals. The optical absorption studies show transmittance improvement in the below gap absorption spectrum. Using variable temperature Hall measurement technique, the shallow defect level on which the penetrating hydrogen makes complex, has been identified. In ‘compensated’ n-type HgCdTe epitaxial layers, hydrogenation can improve the resistivity by two orders of magnitude.

Effect of hydrogenation on the photoluminescence of n-InP

The effect of plasma hydrogenation in nominally undoped n-InP is studied by photoluminescence. The photoluminescence intensity increases after hydrogenation due to the passivation of non-radiative centres. The donor bound exciton luminescence increases by more than two orders of magnitude, pointing to zero or negligible donor passivation in the material. The absence of donor passivation is also indicated by capacitance-voltage profiling of the net donor concentration. The changes in the PL features after hydrogenation are not completely lost even after a 2 min anneal at 425 degrees C.

Structural Dimension Effects of Plasma Hydrogenation on Low-Temperature Poly-Si Thin Film Transistors

The effects of plasma hydrogenation on various N- and P-channel polycrystalline-silicon (poly-Si) thin film transistors (TFT's) fabricated at a maximum temperature of 600° C were analyzed systematically. Device characteristics, such as threshold voltage and field-effect mobility, were improved significantly with hydrogenation time as the channel length of poly-Si TFT's was decreased from 20 µm and 2.5 µm. However, hydrogenation effects on the characteristics of poly-Si TFT's, of which channel width was varied from 2.5 µm to 20 µm, were almost identical. In thin active layer (50 nm) TFT's, the device performance was improved significantly compared with thick (100 nm and 150 nm) devices with hydrogenation time while the thickness of gate poly-Si may not be directly related with hydrogenation effects, probably due to the fact that the hydrogen atoms may diffuse along the channel region while the diffusion of hydrogen atoms through gate poly-Si may be negligible.

Effect of plasma hydrogenation on the defect properties of CuInSe2 single crystals

AbstractThe defect properties of p‐type CuInSe2 single crystals hydrogenated by diffusion from a plasma source are investigated using the Rutherford backscattering/channeling technique and photoacoustic spectroscopy. Plasma hydrogenation is found to produce severe lattice damage, to affect the intrinsic defect equilibrium in the near surface region of the crystals and to create an additional donor. A defect formation model including both defect passivation by hydrogen and damage induced defect creation is proposed to explain the experimental data. The thermal stability of the property modifications is limited to temperatures below about 100 °C.

Effects of Hydrogenation on the Off-State of Polysilicon Thin Film Transistors

ABSTRACTWe have carried out transient photoconductivity experiments on hydrogenated and unhydrogenated polysilicon Thin Film Transistors (TFTs) which indicate that the primary effect of plasma hydrogenation is the reduction by several orders of magnitude of the band tail trapping states. A smaller effect is a reduction of the dangling bond density by a factor of 2 or 3 as indicated by Electron Spin Resonance (ESR) measurements. Since the dangling bond is associated with the generation/recombination center, it may not be obvious how such a small reduction in generation/recombination center density leads to over 2 orders of magnitude reduction in off-state current of the TFTs. In this paper, we describe how the large reduction of band tail states can lead to significant reduction of carrier generation near the contacts despite the fact that the generation/recombination center density is not changed significantly. This reduction of carrier generation leads to the observed reduction in off-state currents.

Doping effects on conductivity and electron spin resonance in post-hydrogenated polycrystalline silicon

The effects of plasma hydrogenation on the electrical properties and electron spin resonance (ESR) are investigated for phosphorus and boron doped polycrystalline silicon films produced by annealing from chemical vapor deposited amorphous silicon. In lightly doped films, the dark conductivity and photoconductivity increase with hydrogenation. The photoconductivity also increases with increasing doping ratio. These increases of the dark conductivity and photoconductivity correspond well to a decrease of ESR spin density due to dangling bonds. In hydrogenated films doped with phosphorus or boron, it is found that the dark conductivity first decreases with increasing doping ratio, and then rapidly increases. These results for the electrical properties and ESR are discussed in terms of the two-phase model in which crystallites with surface bandbending and a damaged layer between the crystallites are included. As a consequence the electrical properties are indicated to have a close relation to the density of dangling bonds in the damaged layer, and the dark conductivity and photoconductivity are controlled by surface conduction of crystallites and a short lifetime of photogenerated carriers in the damaged layer, respectively, depending on the density of dangling bonds. The temperature dependence of the photoconductivity is also discussed based on this model.

Dislocations in germanium: Effects of plasma hydrogenation

Dislocations in germanium: Effects of plasma hydrogenation

Plasma-hydrogenation effects and the thickness dependence of electrical properties and E.S.R. in undoped CVD a-Si

Abstract The effects of plasma hydrogenation on the electrical properties, E.S.R. and optical absorption, and the thickness dependences of these various properties have been investigated for undoped CVD a-Si films. Under plasma hydrogenation at 300°C, the dark conductivity and E.S.R. spin density decrease and the photoconductivity increases with a plasma annealing time of up to 30 min. For the hydrogenated samples, large reductions of these properties and a large enhancement of the activation energy in the dark conductivity are found with a decrease in the film thickness. These results for the electrical properties are analysed with a Schottky-barrier model, and as a consequence their thickness dependences are interpreted by a surface band bending due to positively charged localized states near the free surface which act as recombination centres in photoconduction.

Thickness dependence of electrical and optical properties and E.S.R. in undoped a-Si: H

Abstract The thickness dependence of photo- and dark-conductivities, E.S.R., optical absorption and hydrogen vibrational spectra have been investigated for undoped glow-discharge a-Si: H films. The measurements of the photoconductivity were carried out at wavelengths of 5145 and 6328 and 8500 A. Reductions of photoconductivity and activation energy for dark conductivity, and increases of E.S.R. spin density, the optical energy gap and hydrogen concentration, were found to occur for decreasing film thickness. These results are analysed in terms of a two-layer model and, as a consequence, by the existence of high densities of recombination and E.S.R. centres near the surface(s). The effects of plasma hydrogenation on the photoconductivity and E.S.R., and the photo-induced change of the photoconductivity are discussed in terms of the two-layer model. The photoinduced change is interpreted as a bulk rather than a surface effect.

Plasma-hydrogenation effects on conductivity and electron spin resonance in undoped polycrystalline silicon

The effect of plasma-hydrogenation on the electrical properties and electron spin resonance (ESR) are investigated for undoped polycrystalline silicon films produced by annealing from chemical vapor deposited amorphous silicon. The conduction type for all samples used is p-type. Under a constant plasma annealing temperature, a maximum of the dark conductivity and a minimum of its activation energy are observed at a certain annealing time. This result suggests the presence of two stages in the process of hydrogenation, which is not explained by the models proposed up to now. The ESR spin density decreases and the photoconductivity increases with plasma annealing time, and both are saturated at the first stage. A model for the carrier transport mechanism is proposed in which crystallites with surface bandbending and a damaged layer between the crystallites are included, and the variations of the dark conductivity and photoconductivity are attributed to surface conduction of crystallites and limitation at the damaged layer, respectively, depending on the density of localized states. The temperature dependence of the dark conductivity is also discussed based on this model.