A model for the manganese impurity centre in silicon

Volume 134, number 4

PHYSICS LETTERS A

2 January 1989

A MODEL FOR THE MANGANESE IMPURITY CENTRE IN SILICON S.M. YAKUBENYA and V.V. TUGUSHEV I. V. Kurchatov Institute ofAtomic Energy, Moscow 123182, USSR Received 26 October 1988; acceptedfor publication 28 October 1988 Communicated by V.M. Agranovich

A double-defect model in manganese doped silicon is proposed, explaining the whole spectrum of the deep levels from the same point of view. A possible extension ofthe model to other defects (e.g. antisite centre in GaAs) is discussed.

Manganese impurity in silicon has been studied for a long time, and there is an extensive literature concerning this subject [1—41.However, too many assumptions are made when explaining the behavjour of these impurities in different experiments which are sensitive either to the core electrons (ESR, ENDOR) or to the valence electrons (optical absorption, transport properties). It seems that the Variety of the models proposed (isolated interstitials and substitutionals, four-atom manganese complexes, the manganese—cation pairs etc.) make the state of the art of this problem unsatisfactory. Besides, the apparent similarity between the level positions in manganese doped silicon and the antisite defect in gallium arsenide (fig. 1) makes the problem much more interesting, In this article we propose a description for the im-

purity centre which explains the whole spectrum of the localized levels in a forbidden band of Si: Mn by means of the double-defect model including manganese impurities and silicon vacancies. The change of the Feri level position can result in redistribution of the electron density between the partners and in changing the impurity location relative to the Vacancy site. Electron density localisation either on the impurity atom or on the nearest neighbors corresponds to the extreme cases of an interstitial and a substitutional manganese atom respectively (figs. 2a and 2b). The electron structure and the energy level positions in the forbidden band, connected with the recharging of the impurity atom, differ little, whether this defect is regarded either as due to the isolated interstitial ions or as due to the component of the

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261

Volume 134, number 4

PHYSICS LETTERS A

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double defect. At the same time the behavior of the substitutional impurity is essentially different in the isolated position and coupled with the vacancy. This difference is seen distinctly for the impurity centre, identified by Czaputa et al. [3], as Mn ~ Indeed, treating this centre as the double defect gives two configurations rather than one for the different charge states, depending on the Fermi level position in the forbidden band. The configuration [Mn~ —V2 ~] is realized for EF E~+ 0.05 eV. Besides these centres have different point symmetries (Td for Mn~—V2~], and D2d for [Mn~—V°]). This model allows too the additional possibility of electron density localisation on a single valence bond between the impurity atom and the the vacancy, but with the impurity located in a next nearest interstitial position relative to the vacancy (fig. 3). Such an axial defect [Mn~—V~] having symmetry C 3~can explain the experimental data of ref. [I] without involving the Mn—B centre. This configuration is shown to be metastable, in accordance with the experiment. Other charge states of such a double defect are occupied when changing the Fermi level position by doping the sample with additional donors or increasing the temperature. Finally, note that the apparent similarity between the level position in manganese doped silicon and 262

the antisite defect in gallium arsenide is caused by the equal number of electrons in antibonding orbitals for the centres in one and the same charge state e.g. [Mn?—V°]and [A?~V~a]. A detailed version of the article will be published elsewhere. The authors acknowledge K.A. Kikoin for stimulating discussions. \/Cct1flc~ --

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Volume 134, number 4

PHYSICS LETTERS A

References [I] G.W. Ludwig and H.H. Woodbury, in: Solid state physics, Vol. 13, eds. H. Ehrenreich, F. Seitz and D. Turnbull (Academic Press, New York, 1962) p. 223.

2 January 1989

[2] R. Czaputa, H. Feichtinger and J. Oswald, Solid State Commun. 47 (1983) 223. [3] R. Czaputaetal., Phys. Rev. Lett. 55 (1985) 758. [4] F. Beeler, O.K. Andersen and M. Shuffler, Phys. Rev. Lett. 55 (1985) 1498. [5] N.T. Bagraev et al., JETP Lett. 45 (1987) 231.

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