Electronic Structure of Vacancy-Phosphorus Impurity Complexes in Silicon
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ELECTRONIC STRUCTURE OF VACANCY-PHOSPHORUS IMPURITY COMPLEXES IN SILICON HONGQI XU" AND U. LINDEFELT** *Dcpartmlent of Theoretical Physics, University of Lund, S6lvegatan 14A, S-22:3 62 Lund. Sweden **Asea Brown Boveri Corporate Research, S-721 78 Vaisteris, Sweden
ABSTRACT N\e present a systematic theoretical investigation on four vacancy-phosphorus itipurity Complexes in silicon, i.e., a vacancy with one through four phosphorus impurities oil the nearest neighbour sites of the vacancy, using a semi-empirical self-consistent tight-I)indilg theory. The calculations are based on the Lanczos-Haydock recursion Green's function method. The predicted energy levels in the band gap for the five cases, the isolated Si vacancy and the four complexes. show a remarkable regularity. We shed light on this regularity by relating it to the localization of the wavefunctions on the Si and P atoms surroun(ling the vacancy. WVecompare our results with experimental work. Introduct ion Int many semiconductor compounds, especially in high power components like t hyristors. charge carrier lifetime is controlled by vacancy- and divacancy-related defects created b% electron irradiation. It is strongly suspected that the carrier lifetime is controlled to a large extent by an interplay between doping (for instance with phosphorus atoms) and vacancies / divacancies created by the electron irradiation. Therefore, there is an interest from manufacturers of power components to understand better the int.eract iou bet ween a
vacancvy and l)hosphorus atoms. Experimentally, some vacancy-phosphorus impurity complexes in Si were identified. Watkins and Corbett [1] thoroughly investigated the phosphorus-vacancy complex (V-P, or E-center) with EPR and ENDOR in 1964. The electronic structure of the defect in its neutral charge state was derived. The defect in its negative charge state was studied by Kimerling and his co-workers in 1975 [2]. More recently, positron-annihilation spectroscopy [3] and the hydrostatic pressure technique [4] have also been used to study the defect. The phosl)horus-vacancy-phosphorus complex (V-P 2 ) in its p)ositive charge. state was identified by Sieverts and Anmnerlaan [5] using the EPR technique. The defect comt)lexes involving more than two phosphorus atoms have not been identified so fair. Hlowever. a very recent work [6] shows that there may exist such a complex in heavily P-doped Si. In this paper, we report a theoretical investigation on the electronic structure of four neutral vacancy (V)-phosphorus impurity complexes. V-P 1 . V-P 2 , \'-P3, and V\'-P4- in Si. The effect of lattice distortion is discussed. Coomparison of our results wit I experiinemital work is l)resented. TlIeorv The calculations are based on a semi-empirical self-consistent tight-binding met hod. The perfect crystal is described by an ,;p3 first and second nearest neighbour tight-biiidling Hamiltonian [7] in a supercell containing 2662 Si atoms [8]. A vacancy is simply created
Mat. Res. Soc. Symp. Proc. Vol. 163. ©1990 Materials Research Society
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