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| 1.
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Zhou, Jiang-Huai ; Kumeda, Minoru ; Shimizu, Tatsuo
概要:
金沢大学大学院自然科学研究科電子物性デバイス<br />金沢大学工学部<br />We report on a detailed investigation of the spatial distribution of dangling b
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onds (DB's) in light-soaked hydrogenated amorphous silicon (a-Si:H) films. The results for light soaking at different light intensities (3 W/cm2 and 300 mW/cm2) show that the inverse power-law DB distribution, Nυ(x)=Cυx-α, holds regardless of the light soaking intensity. Here, Nυ(x) is the volume density of DB's at depth x measured from the surface, and Cυ and α(≈0.6) are constants. The nonuniform spatial distribution of DB's in light-soaked a-Si:H is thought to originate from a nonuniform distribution of photocarriers during light soaking rather than from an inhomogeneity of the material. The same annealing behavior of light-induced DB's was observed regardless of the thickness of the sample and regardless of whether the sample was light soaked from one side or from both sides. This result, together with the observation of identical spin characteristics, indicates that the light-induced DB's at various depths of a given a-Si:H sample are identical in nature. The surface DB density is found to be much less sensitive to light soaking than the bulk DB density and can be assumed unchanged if the light-soaking intensity is not much higher than 300 mW/cm2 and the light-soaking time is shorter than ∼10 h. We show that the conventional method of estimating the surface DB density is no longer appropriate for light-soaked a-Si:H, due to the highly nonuniform distribution of DB's in the material. The nonuniform distribution of DB's can lead to significant disagreements between different techniques in quantifying the Staebler-Wronski effect and should therefore be taken into account in studies of the SW effect.
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| 2.
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Li, Ying ; Zhong L., Zhi ; Hua Chen, Guang ; Kumeda, Minoru
概要:
金沢大学大学院自然科学研究科電子物性デバイス<br />金沢大学工学部<br />We have constructed a hot-wire-assisted ECR-CVD system to prepare a-Si:H and μc
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-Si:H films. The effect of hot wire (HW) temperature on crystallization of a-Si:H films is studied in the films prepared by this system. At low HW temperature, about 20 at.% hydrogen is included in the film. With increasing the HW temperature, the contents of the total hydrogen, SiH2 and SiH decrease, and the microcrystalline phase appears. It is found from the area of the TO peak of the Raman scattering spectra that the volume fraction of the crystalline phase increases with increasing the HW temperature. The crystalline peak has a tendency to shift toward the higher wavenumber with increasing the HW temperature, suggesting that the grain size increases with increasing the HW temperature. © 2006 Materials Research Society.
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| 3.
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Nádaždy, V. ; Durń, R. ; Thurzo, I. ; Pinčík, E. ; Nishida, A. ; Shimizu, J. ; Kumeda, Minoru ; Shimizu, Tatsuo
概要:
金沢大学大学院自然科学研究科電子物性デバイス<br />金沢大学工学部<br />Results of charge deep-level transient spectroscopy (DLTS) and electron spin re
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sonance (ESR) measurements on undoped hydrogenated amorphous silicon (a-Si:H) clearly demonstrate that a group of gap states with a mean energy of 0.82 eV as observed in charge DLTS experiments for a-Si:H based metal/oxide/semiconductor structure is the same as the g=2.0055 ESR defect (the Dz component). This correlation provides a distinct marker for charge DLTS technique. We obtained a very good fit to spectra obtained on undoped a-Si:H in the annealed state whilst there is some discrepancy between the experimental and simulated spectra for the light-soaked state. The first quantitative comparison of defect pool model with gap states directly observed by charge DLTS offers not only additional data for more accurate identification of all the intrinsic and light-induced defects. This also renders distinct counter-evidence to recently published conjectures about the creation of another charged defect during early stage of Staebler-Wronski effect. By contrast, our presented results clearly argue for opposite process, i.e., decay of positively charged defect states Dh.
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| 4.
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Kumeda, Minoru ; Sekizawa, Yoshitaka ; Morimoto, Akiharu ; Shimizu, Tatsuo
概要:
金沢大学大学院自然科学研究科電子物性デバイス<br />金沢大学工学部<br />The crystal-field potential at the Er3+ ion surrounded by six oxygen ions is ex
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panded in terms of polynomials. After converting it into equivalent angular momentum operators, the Stark-splitting of the 4I15/2 ground state of the Er3+ ion is calculated. Influence of the change in the environment of the Er3+ ion on the shift of the energy levels is investigated and compared with the observed Er photoluminescence spectrum in a-Si:H. The scattering of the calculated energy levels by the structural fluctuation around the Er 3+ ion is also compared with the linewidth of the component photoluminescence lines. © 2006 Materials Research Society.
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| 5.
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Morimoto, Akiharu ; Takizawa, Hidetoshi ; Yonezawa, Yasuto ; Kumeda, Minoru ; Shimizu, Tatsuo
概要:
金沢大学工学部<br />Silicon oxide films were prepared at room temperature by pulsed laser ablation using an ArF or KrF excimer
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laser in a gas mixture of He and O2. The effect of an ArF excimer laser irradiation on the deposited film was investigated. As-deposited transparent films containing Si crystallites with sizes greater than 10 nm show photoluminescence. However, after laser irradiation with 1000 shots, the photoluminescence (PL) intensity was increased by two orders of magnitude. The PL spectrum is centered around 570 nm (2.2 eV). The origin of the large PL enhancement is discussed
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| 6.
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Zhang, Qing ; Takashima, Hideki ; Zhou, Jiang-Huai ; Kumeda, Minoru ; Shimizu, Tatsuo
概要:
金沢大学理工研究域<br />We report on the effects of intense light soaking at room temperature (RT) and at 77 K on the defect dens
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ity in hydrogenated amorphous silicon (a-Si:H). It is found that at short light-soaking times, light soaking at RT is more efficient in creating metastable defects than at 77 K. With increasing light-soaking time, however, 77-K light soaking causes the defect density to increase at a higher rate than does RT light soaking. There are signs that the saturated value of the defect density for 77-K light soaking is larger than that for RT light soaking. Qualitatively, a correlation exists between the increase in the defect density and the decrease in the photoconductivity; however, an inverse proportionality is not observed between the photoconductivity and defect density. For a given defect density, the photoconductivity is smaller for 77-K light soaking than for RT light soaking. The defects generated by 77-K light soaking are found to be stable at 77 K. However, significant annealing of defects occurs after raising the sample temperature to RT. Light-induced annealing of defects is also observed. We explain our results by adopting the views that there is a broad distribution of defect-annealing activation energies and that the defects with small annealing activation energies are more effective recombination centers than those with large annealing activation energies. We show that many other related experimental results can also be accounted for by the above views. © 1994 The American Physical Society.
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| 7.
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Shimizu, Tatsuo ; Iwami, Masafumi ; Okagawa, Toshio ; Morimoto, Akiharu ; Kumeda, Minoru
概要:
It is found in a-Si:H and N-doped a-Si:H that the ESR spin density N, increases and saturates with light-soaking slower than the dark-and photoconductivities (ad and ap) do. In the recovery process by annealing, the change in N. also
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occurs slower than ad and up. From the measurement of the activation energy for 9d the change in ad is found to originate mainly from the movement of the Fermi level EF. In order to elucidate the origin of different behaviors between N, and ad or ap, the light-induced ESR and the constant photocurrent method measurements have been carried out.
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| 8.
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Kumeda, Minoru ; Takahashi, Yukio ; Shimizu, Tatsuo
概要:
Fluorinated amorphous silicon (a-Si:F) films are prepared by three different methods: glow-discharge decomposition of SiF2 gas, magnetron sputtering, and conventional diode sputtering. The incorporation scheme of F atoms is
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investigated by means of nuclear magnetic resonance (NMR) and infrared (ir) absorption measurements. 19F NMR signals observed at 4.2 K can be simulated by superposing signals from dispersed F atoms, clustered F atoms, SiF4 molecules, and SiF3 species. The content of SiF4 increases by annealing in agreement with an increase in the intensity of ir absorption at 1020 cm-1. 19F NMR signals at 77 K and at room temperature show the effect of motional narrowing because SiF4 molecules move easily in the amorphous network.
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| 9.
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Morimoto, Akiharu ; Matsumoto, Minoru ; Yoshita, Masahiro ; Kumeda, Minoru ; Shimizu, Tatsuo
概要:
O, N, or C impurity was separately incorporated into a‐Si:H films by hot‐wall glow discharge decomposition. The effect o
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f the impurity incorporation was investigated by electrical and electron spin resonance measurements. Both O and N impurities were found to increase the dark conductivity by decreasing its activation energy in a‐Si:H films. Furthermore, it was found that O and N impurities delay the photoresponse. C impurity, however, has no appreciable effect on them. These findings suggest that O and N impurities shift the Fermi level upward and form a trapping state for photoexcited electrons, supporting our O+3 and N+4 model.
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| 10.
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Yan, H. ; Morimoto, Akiharu ; Kumeda, Minoru ; Shimizu, Tatsuo ; Yonezawa, Yasuto
概要:
Surface oxidation and surface defect creation processes in a-Si:H films have been studied in detail by means of electron spin resonance(ESR) and X-ray photoelectron spectroscopy(XPS). It is found that Si dangling bonds created by
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the surface oxidation distribute far wider than the thickness of the SiO2 layer. These defects are also found to be removed out by annealing at around 100cC. These defects are proposed to be created by a stress in a-Si:H induced by the surface oxidation. Moreover, the presence of the surface defects unrelated to oxidation is shown for the first time by the present experiment. The origin of these defects, however, are not clear at present.
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