Mechanism of Defect Reactions in Semiconductors
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1195-B02-02
Mechanism of Defect Reactions in Semiconductors Yuzo Shinozuka Faculty of Systems Engineering, Wakayama University, Sakaedani 930 Wakayama, 640-8510, Japan ABSTRACT Proposed mechanisms so far on defect reactions in semiconductors are reexamined. Structural instability of point defects is explained in terms of the Jahn-Teller effect. It is found that the tetrahedral coordinated bonds, which do not have inversion symmetry, are not so rigid as we consider, especially for hole localization. Second topic is the phonon-kick mechanism for defect reactions under carrier injection. In order to discuss this mechanism in detail, we recall the configuration coordinate (c-c) diagram, which is often misunderstood in the literature. The proper relation is explained among the lattice distortion, the position of the electronic level in the band gap (thermal and optical depths), the total energy the multiphonon (e and h) carrier capture processes and the following induced lattice relaxation. A numerical simulation has been performed on phonon kick mechanism. It is found that a rapid increase of the transient lattice vibration around the defect is possible and the probability critically depends on the carrier concentrations and the phonon frequency distribution.
INTRODUCTION Nonradiative recombination of electron and hole in semiconductors occurs via either Auger process or multiphonon process. The latter takes place at deep-level defects and limits the efficiency of light emitting devices and is also considered as a cause of degradation of optical devices such as solar sells, light emitting diodes and lasers. In order to improve the efficiency of these devices and establish their reliability, the mechanism of various electro-atomic process such as structural change at a defect, impurity diffusion, dislocation climb and glide motion [1, 2] should be elucidated. In the present paper we will discuss two topics. One is structural instability of point defects, which will be explained in terms of the Jahn-Teller effect. It is found that the tetrahedral coordinated bonds, which do not have inversion symmetry, are not so rigid as we consider, especially for hole localization. Second topic is phonon-kick mechanism for defect reactions under carrier injection. During nonradiative multiphopnon recombination of an electron and a hole electronic energy (~ the band gap) is converted to the lattice kinetic energy, which is considered to promote defect reactions. In order to discuss this mechanism in detail, we will recall the configuration coordinate (c-c) diagram, which is often misunderstood in the literature. The proper relation is explained among the lattice distortion, the position of the electronic level in the band gap (thermal and optical depths), the total energy the multiphonon (e and h) carrier capture processes and the following induced lattice relaxation. Finally we will show results of a numerical simulation on the phonon kick mechanism. It is found that a rapid increase of the transient lattice vibration around the defe
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