Structural and Optical Features of Nano-Crystalline Silicon Films Prepared by PECVD and RF Magnetron Sputter Techniques
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STRUCTURAL AND OPTICAL FEATURES OF NANO-CRYSTALLINE SILICON FILMS PREPARED BY PECVD AND RF MAGNETRON SPUTTER TECHNIQUES M.-B. Park and N.-H. Cho Department of Materials Science and Engineering, Inha University, Inchon 402-751, Korea, [email protected] ABSTRACT Nano-crystalline Si films were prepared by plasma enhanced chemical vapor deposition (PECVD) and rf-magnetron sputter techniques at various deposition conditions, and the relations of the photoluminescence (PL) phenomena of the films with process variables are discussed. The phase of the films prepared at R.T. by PECVD techniques is somewhere between amorphous and crystalline states, consisting of nano-crystallites of size ranging from 3.2 to 5.3 nm. These films exhibit significant PL intensities near blue light region; the PL peaks shift from 510 to 460 nm with decreasing the reaction gas (SiH4) fraction from 4.7 to 2.0%. The films prepared at 500 by PECVD are composed of about 5 and 150 nm crystallites, exhibiting little PL phenomena. The PL intensity of the films prepared by sputter techniques was observed to increase with raising the sputter power and the post-deposition heat-treatment temperature. INTRODUCTION Since the discovery of photoluminescence (PL) phenomena from porous silicon, nanocrystalline Si (n-Si) semiconductors have attracted much more attention in optoelectronic industry, integrated photosensors and imaging device applications, because of their unique and useful physical properties [1]. These materials can also be easily compatible with the Sibased integrated electronic circuits [2]. An increasing number of experiments on the synthesis of these materials have been carried out by various fabrication techniques such as chemical vapor deposition (CVD), sputter, etc [3]. Many researches have also been performed for the understanding of the PL phenomena of nano- and meso-porous bulk Si [4-6]. Optical characteristics of n-Si films have been reported by several groups [7], revealing that these properties are critically determined by nano- and meso-structure of the Si films. However, very little experimental reports have been published on the structural identification of the n-Si films prepared by plasma enhanced CVD (PECVD) and physical vapor deposition [8]. It is indispensable to understand the relations of the nano- and meso-structure with the PL phenomena for fine control of the physical characteristics of the films. In this study, we investigated the nano-structural features and optical characteristics of nSi films as a function of deposition parameters and post-deposition heat-treatment conditions, which were prepared by PECVD and rf magnetron sputter techniques, and discussed the relations of the PL phenomena of the films with process variables. EXPERIMENTAL PROCEDURE PECVD and RF magnetron sputter techniques were used to prepare Si thin films on silicon wafer and soda-lime-silicate glass, respectively. The reaction gas fraction S(%) in following equation (1) is the ratio of SiH4 to carrier gases inserted into the reaction chamber. S% = SiH4
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