Photo-stimulated Rebuilding of Structure in Semiconductors
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Photo-stimulated Rebuilding of Structure in Semiconductors Rashidova S.S., Oksengendler B.L., Turaeva N.N., Aripov I.M. Institute of Polymer Chemistry and Physics, Uzbekistan
Abstract A strong electron-phonon interaction observed in semiconductors allows to realize a special kind of atomic rebuilding under photo-irradiation of the medium. We consider three types of defective structures: one atomic, two-atomic (“dump-bell”) and multiatomic (kinks) defects. It is shown that an inversion effect of the defect potential term may be realized if there are non-equivalent neighboring positions of one-atomic and two-atomic defects. In this case the photo-excitation of electronic subsystems of these defects leads to an inversion of potential terms and a consecutive athermal rebuilding of the defective structures. The Yahn-Teller effect and psevdo-effect play a special role here. It is shown for kink-structures that the photo-excitation of the electronic subsystems results in the alteration of kink nonius and the successive exponentially strong decrease of an activation barrier. Especially effects of athermal atomic rebuilding of U-negative defects are considerable.
Introduction
The possibility of stimulating atomic processes with electronic excitations is a new aspect of defect process physics. After the excitation of electronic subsystem the relaxation of this energy to the atomic degrees of freedom can lead to the atomic rebuilding with certain probability. Electron-stimulated atomic rebuildings (ESAR) [1,2] based on a strong electron-phonon interaction are well known in semiconductors of covalent and ionic characters.
Types of such electronic-stimulated atomic
rebuildings are rather wide and they can be subdivided into the small-scale and largescale ones according to the quantity of defects involved into the atomic processes. In this work three models of ESAR based on different defects are considered in such systems.
H9.11.1
Body
1. Photo-stimulated diffusion of one-atomic defect
Let us consider one-valent positively charged impurity atom (or host interstial atom) introducing a deep local level into the forbidden band of electronic spectra. At photo-irradiation free electron and hole are produced. This electron could be trapped on the deep local level and deform the crystal around it. The impurity atom is suggested to interact with neighbor host atoms with the following potential U (r ) = U rep (r ) + U attr (r ),
(1.1)
where Urep(r) is the repulsive energy between the ion and the neighbor host atoms, Uattr(r) is the attractive energy between them. The total energy of the “crystal + impurity” system for two sites of symmetry with respect to the neighbor host atoms is defined by the formulas (1) (1) (r ) + U attr (r ) U (1) (r ) = U rep
(1.2)
(2 ) (2 ) (r ) + U attr (r ) U (2 ) (r ) = U rep
The activation energy of defect for its diffusion will then be given by [3] ∆Qm = U (1) (r ) − U ( 2 ) (r ) = ∆U rep (r ) + ∆U attr (r )
(1.3)
Urep(r) is estimated by means of Born-Mayer`s equation:
U rep (r ) = Ae
rL +
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