Microstructure Characterization of Amorphous Silicon Based Alloys by Inert Gas Effusion Studies
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Microstructure Characterization of Amorphous Silicon Based Alloys by Inert Gas Effusion Studies Wolfhard Beyer1, Sergio S. Camargo, Jr.2 and Rosari Saleh3 1 Institut für Schicht- und Ionentechnik, Forschungszentrum Jülich, D-52425 Jülich, Germany 2 Programa de Engenharia Metalúrgica e de Materiais, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, CEP 21945-970, Brazil 3 Jurusan Fisika, Fakultas Matematika dan Ilmu Pengetahuan Alam, Universitas Indonesia, Depok 16424, Indonesia ABSTRACT It is shown that inert gas effusion employing implanted neon and argon atoms is a useful tool for microstructure characterization of a-Si based alloys. The method measures sensitively interconnected voids and gives information about sizes of microstructure. Limitations of the method are discussed. The results show network reconstruction effects in a-Si:O:H and a-Si:C:H alloys as a function of annealing. INTRODUCTION One major defect in amorphous hydrogenated silicon (a-Si:H) based alloys is an interconnected void structure [1]. While voids and microstructure can be detected in a-Si:H and related alloys by various techniques including small angle scattering [2] and infrared absorption [3], hydrogen effusion is particularly sensitive to interconnected void structures. Such structures result in a characteristic hydrogen effusion maximum, denoted as low temperature process, arising from desorption of hydrogen from void surfaces, followed by rapid outdiffusion of H2 [4]. However, hydrogen effusion experiments give little information about void sizes apart that only network openings are detected which are wide enough to allow long range motion of H2. In order to get more information about void sizes, it is of interest to study diffusion or effusion of inert gas atoms. Since these atoms do not react with silicon, their diffusion or effusion characteristics are expected to be related to the sizes of network openings and interconnected voids. Indeed, the motion of inert gas atoms has been used for the characterization of network openings in glasses [5]. Outdiffusion of implanted inert gas ions has also been studied for (device-grade) a-Si:H by Beyer [4]. It was found that only He effuses at temperatures when the material was still amorphous while larger inert gas atoms effuse only at higher temperatures. Work by Jech and Kelly [6] suggested that the high temperature effusion of implanted inert gas is at least partially related to crystallization effects. Here, we report a study of Ne and Ar effusion for several series of a-Si:C:H and a-Si:O:H samples which were implanted with Ne and Ar ions.
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EXPERIMENT The films investigated involved three series of a-Si:C:H films, two (one silicon-rich and one carbon-rich) deposited in (capacitive) rf glow discharge systems from SiH4-CH4 gas mixtures and one (silicon-rich) deposited by dc magnetron sputtering using a silicon target and Ar-CH4 mixtures as a sputtering gas. A series of a-Si:O:H films was deposited by rf glow discharge from SiH4-CO2 gas mixtures. The deposition conditions o
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