Hydrogen Diffusion in N-Type Silicon.Comparison With P-Type Silicon
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HYDROGEN DIFFUSION IN N-TYPE SILICON. COMPARISON WITH P-TYPE SILICON R. RIZK*, P. de MIERRY*, D. BALLUTAUD*, M. AUCOUTURIER* D. MATHIOT** * Laboratoire de Physique des Solides de Bellevue - CNRS, 1 Place A. Briand - 92195 Meudon Cddex, France. ** CNET-CNS, BP 98 - 38243 Meylan Cddex, France.
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ABSTRACT Deuterium diffusion profiles in medium phosphorus doped silicon (1016 and 1017 cm"3) at two different deuteration temperatures (120 and 150°C) are simulated with an improved version of a previously reported model. The new approach which excludes the H2 molecule formation, as applied recently to ptype silicon, allows the determination of kinetic and thermodynamic parameters such as diffusion coefficients, activation and dissociation energies. These parameters 6re compared with those found for p-type silicon and discussed in the light of available data for n-type material. INTRODUCTION During the past years, the important role assigned to incorporated hydrogen in crystalline silicon has stimulated an intense activity concerning its diffusion processes, charge states, microscopic structures and passivation effects in this material [1]. In an analogous approach of the well established positively charge state of hydrogen in p-type silicon [2], which acts as a deep donor near mid-gap [3], it was suggested that the stable charge state of H in n-type silicon could be H" with an acceptor level in the gap (4]. While earlier papers reported slightly passivating effects of H in n-type silicon [5], and a more evident complex formation of H with n-dopants [6], the experimental evidence of negatively charge state of H in this material has been presented recently by Tavendale et al. (7] and Zhu et al. (8]. These recent informations are consistent with the assumptions of the diffusion model previously reported by one of us [9], where it is assumed that in n-type silicon, the charge state H- with a deep acceptor level Ea in the gap can react with the ionized n-dopant to form neutral complexes. We have recently shown [10] that the formation of H2 molecules must be totally neglected at the diffusion temperature in order to obtain good simulations in medium B-doped silicon. Indeed, we have found that it is the only way to accurately simulate the shoulder existing in the profiles between the very near surface layer - where the high H concentration is due to trapping on plasma damage - and the H plateau at the dopant concentration. Good simulations were then obtained by assuming neutral deuterium diffusion and H-dopant interaction. In n-type Si, the deuterium profiles exhibit also a region where the deuterium concentration exceeds the dopant concentration by at least an order of magnitude, also reported previously [4,5,7]. In fact, it turns out that, this region is analogous to the shoulder region observed in p-type Si. We propose then in this paper a description of H diffusion in medium phosphorus doped Si (1016 and 1017 cm- 3 ), where passivation effects and H- evidence are reported [7,8], based on the same kind of assumption as in m
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