The Micro-Structure and Electron Conduction Mechanism of Hydrogenated Nano-Crystalline Silicon Films
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THE MICRO-STRUCTURE AND ELECTRON CONDUCTION MECHANISM OF HYDROGENATED NANO-CRYSTALLINE SILICON FILMS
YULIANG HE,1 YIMING CHU,§ HONGYI LIN* AND GUOGUANG QINt IThe Amorphous Physics Research Laboratory, Beijing University of Aeronautics and Astronautics, Beijing 100083, P.R. China. tBeijing Laboratory of Electron Microscopy, Chinese Academy of Sciences, Beijing 100080, P.R. China. t Department of Electronic Engineering, Beijing Institute of Technology, Beijing 100081, P.R. China. 'Department of Physics, Peking University, Beijing 100871, P.R. China.
ABSTRACT The hydrogenated nano-crystalline silicon (nc-Si:H) films have been deposited with PECVD method.. 2 The micro-structure of these films has been studied by TEM and HREM. The PECVD nc-Si:H films show fiber texture structure which is exceptional compared with the nano-size materials made by the method of compressing granules method. The fractal dirnention of this texture structure has been calculated with a Fourier filtered image. The relationshisps between conductivity and temperature and micro-structure has also been studied and the mechanism of electron conduction is discussed.
Introduction
In last 10 years, the nano-crystalline (nc) materials have been extensively developed in a series of materials sciences fields due to their peculiar properties. However, in the field of semiconductor materials not many reports have been published until now. ' 4 In recent years, we have successfully fabricated2 the nc-Si:H films by PECVD method under accurately controlled the deposition conditions.'' Usually the nano-crystalline materials are prepared by compressing and sintering method or colloidal method? With our technology the nc-Si:H can be deposited directly into films. It is particularly valuable for some devices, for example, a nano-crystalline silicon fihlm sensor. In this paper, the micro-structural properties of these nc-Si:H films have been studied by TEM and HREM methods. The fractal dimension of the texture structure has been calculated with a Fourier filtered image, and the conduction mechanism has also been studied.
The micro-structure of nc-Si:H films
The nc-materials consist of two parts: a mass of a few to 10 nano-meter granules (crystalline phase) and an interfacial region (grain boundaries and inter-grain phase). The latter part has significant influence on the property of nc-materials. We have studied the structure Mat. Res. Soc. Symp. Proc. Vol. 283. 01993 Materials Research Society
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properties of a series of nc-Si:H films by Raman scattering and X-ray diffraction methods in a previous paper. 2 We obtained the mean grain size d = 3--5 nm and the crystalline volume fraction X, = (50±5)%. Four TEM cross-sectional samples of nc-Si:H films on glass substrates have been prepared and examined in a Philips 430 microscope operated at 300 kV. Fig.1 shows a typical micrograph of these samples with its electron diffraction(ED) pattern. Fig.la is a central dark field image, and the aperture is centered at one of the strong reflections. Bright areas show c
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