In Situ Probing and Atomistic Simulation of a-Si:H Plasma Deposition
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In Situ Probing and Atomistic Simulation of a-Si:H Plasma Deposition Eray S. Aydil1, Dimitrios Maroudas1, Denise C. Marra1, W. M. M. Kessels2, Sumit Agarwal1, Shyam Ramalingam1, Saravanapriyan Sriraman1, M. C. M. Van de Sanden2, and Akihiro Takano1,3 1 Chemical Engineering Department, University of California Santa Barbara, Santa Barbara, CA 93106, U. S. A. 2 Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 3 Permanent Address: Fuji Electric Corporate Research and Development, Ltd., 2-2-1, Nagasaka, Yokusuka-City 240-0194, Japan ABSTRACT Hydrogenated amorphous silicon thin films deposited from SiH4 containing plasmas are used in solar cells and thin film transistors for flat panel displays. Understanding the fundamental microscopic surface processes that lead to Si deposition and H incorporation is important for controlling the film properties. An in situ method based on attenuated total internal reflection Fourier transform infrared (ATR-FTIR) spectroscopy was developed and used to determine the surface coverage of silicon mono-, di-, and tri-hydrides as a function of deposition temperature and ion bombardment flux. Key reactions that take place on the surface during deposition are hypothesized based on the evolution of the surface hydride composition as a function of temperature and ion flux. In conjunction with the experiments, the growth of a-Si:H on H-terminated Si(001)-(2×1) surfaces was simulated through molecular dynamics. The simulation results were compared with experimental measurements to validate the simulations and to provide supporting evidence for radical-surface interaction mechanisms hypothesized based on the infrared spectroscopy data. Experimental measurements of the surface silicon hydride coverage and atomistic simulations are used synergistically to elucidate elementary processes occurring on the surface during a-Si:H deposition. INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) films deposited using SiH4 plasmas are used as the active layer in photovoltaics and thin film transistors (TFTs). In the photovoltaic arena, recent research on a-Si:H films for solar cells focuses on depositing at very low temperatures (
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