Density-Functional Theory Study of Hydrogen Induced Platelets in Silicon
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Density-Functional Theory Study of Hydrogen Induced Platelets in Silicon Liviu Bîlteanu1,2 and Jean-Paul Crocombette1 1 Commissariat à l’Energie Atomique et Alternative, 91191 Gif-sur-Yvette Cedex, France. 2 Laboratoire de Physique des Solides UMR 8502, Université Paris Sud 91405 Orsay Cedex, France. ABSTRACT In this contribution we present the results of Density-Functional Theory (DFT) calculations of platelets as modelled by infinite planar arrangements of hydrogen atoms and vacancies in (100) planes of silicon. From the observation of the relaxed platelet structures and the comparison of their energy with the one of hydrogen molecules dissolved in silicon we were able to evidence several features. A planar arrangement of hydrogen atoms inserted in the middle of Si-Si bonds proves unstable and Si bonds must be broken for the platelet to be stable. In the (100) plane the most stable configuration is the one with two Si-H bonds (a so-called SiH2 structure). It is possible to generate SiH3 structures which are more stable than hydrogen dissolved in Si bulk but less than SiH2 structures but SiH1 or SiH4 sometimes observed in experiments prove unstable. INTRODUCTION Hydrogen induced platelets (HIPs) are bidimensional defects involving 1-2 atomic plans occuring in hydrogen implanted samples of silicon [1] or of some other materials[2]. HIPs have been observed mostly on (100) or (111) plans, being generally oriented within the plans parallel to the implantation surface of the sample [3-4]. Yet, the HIP orientation depends not only on the crystallographic features of the sample but also on the implantation conditions: different implantation conditions can induce different stress gradients into the sample that can influence the orientation of HIPs [5-6]. Several experimental papers have been published related to the occurrence and growth of HIPs (see for example [7] and the references mentioned therein). Despite the fact that some theoretical works have been published on the structure of HIPs [8-10] there are some open issues related to the HIPs structure and their formation mechanisms. In this paper we present several HIPs models that we have studied by more accurate DFT calculations that have been performed before. We focus on the (100) structures and on their stability in the hydrogen supersaturation conditions. The remaining of this paper is organized in three sections. In the section 2 we shall present the computational details, the methods of the structure generation and the formulas we have used to calculated the formation energies for the generated structures. In the section 3 we present the results we have obtained. Finally, in the last section we shall summarize and draw the conclusions. THEORY All the DFT calculations presented in this paper have been performed with the SIESTA code [11] using norm-conserving pseudopotentials and bases of numerical atomic orbitals. The exchange-correlation functional we have used is the Generalized Gradient Approximation (GGA) [12]. The pseudopotentials were provided with the SIE
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