Microstructure of the Silicon Film Prepared Near the Phase Transition Regime from Amorphous To Nanocrystalline
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Microstructure of the Silicon Film Prepared Near the Phase Transition Regime from Amorphous To Nanocrystalline Shibin Zhang, Xianbo Liao, Yanyue Xu, , Zhihua Hu, Xiangbo Zeng, Hongwei Diao, Muchang Luo, and Guanglin Kong State Key Laboratory for Surface Physics, Center of Condensed State Physics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China. ABSTRACT:
A kind of hydrogenated diphasic silicon films has been prepared by a new regime of plasma enhanced chemical vapor deposition (PECVD) near the phase transition regime from amorphous to nanocrystalline. The microstructural properties of the films have been investigated by the micro-Raman and Fourier transformed Infrared (FT-IR) spectra and atom force microscopy (AFM). The obtained Raman spectra show not only the existence of nano-scaled crystallites, but also a notable improvement in the medium-range order of the diphasic films. For the FT-IR spectra of this kind of films, it notes that there is a blueshift in the Si-H stretching mode and a redshift in the Si-H wagging mode in respect to that of typical amorphous silicon film. We discussed the reasons responsible for these phenomena by means of the phase transition, which lead to the formation of a diatomic hydrogen complex, H2* and their congeries.
INTRODUCTION: The light-induced degradation of a-Si:H, referred to as the Staebler-Wronski
effect, makes a big obstacle toward a fruitful application of the material [1]. Although intensive research has been carried out, since its discovery, to elucidate the mechanism of this effect, a broad agreement has not been achieved until now. It has been gradually realized that the metastable properties of a-Si:H film is closely related with the amorphous network and vast hydrogen atoms within the film, therefore in order to improve its stability the microstructure of the film must be ameliorated [2-7]. From the thermal dynamics point of view, improvement in the microstructure will eventually lead to microcrystallization, as a result the high photosensitivity and high absorption coefficient, which is intrinsic for amorphous silicon, will be invalid simultaneously. Thus, we proposed that the film should be prepared near the phase transition regime from amorphous to microcrystalline to obtain both the fine photoelectronic property and the high stability at the same time [8]. The tenet of this paper is to prepare silicon film with high stability in phase transition regime by adjusting the plasma parameters, and to study its structural and photoelectronic properties as well as its light-induced changes.
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EXPERIMENTAL DETAIL The stable diphasic a-Si:H films were prepared by using the ‘uninterrupted growth/annealing’ PECVD technique [9]. By using the highly dilute saline gas, the hydrogen dilution ratio (RH=[H2]/[SiH4]) between 50 and 100, and a relatively high-power density 100mW/cm2, the deposition regime was chosen to be adjacent or just above the phase transition from amorphous to crystalline state. For comparison, some a-Si:H sam
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