Feedback and Inflation Mechanism in Successive Multiphonon Carrier Captures at Deeplevel Defects
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Feedback and Inflation Mechanism in Successive Multiphonon Carrier Captures at Deeplevel Defects Kei Suzuki, Masaki Wakita and Yuzo Shinozuka Faculty of Systems Engineering, Materials Science and Chemistry, Wakayama University, 930 Sakaedani, Wakayama 640-8510, Japan ABSTRACT Possibility of feedback and inflation mechanism among carrier captures by a deep-level defect and transient induced lattice vibrations is discussed using proper configuration coordinate diagrams for many carriers. Treating the lattice motion classically we selfconsistently simulate the time evolution of the interaction mode and a series of athermal captures of electron(s) and hole(s). When both the activation energies Eacte and Eacth are small, a series of successive athermal captures is enhanced and probable for high carrier densities, however, we find that the possibility of inflation in the amplitude of the lattice vibration critically depends on the minority capture rate and the relative width of the phonon frequency distribution. INTRODUCTION Some deep-level defects in semiconductors act as a nonradiative recombination center and limit the efficiency of light emitting devices, called killer center. There are two major nonradiative processes: one is Auger process by exciting another carrier, and the other is multiphonon process by emitting phonons. The latter is very serious in light emitting devices since the electronic energy is converted to phonon energy (multiphonon process), which is considered to be a trigger of defect reactions, known as phonon kick mechanism [1, 2]. A nonradiative recombination at a defect consists of a pair of successive captures of an electron and a hole. For example, in p-type semiconductors a minority electron is first captured by a defect, usually showing the Arrhenius type probability with the thermal activation energy Eacte. After the capture the lattice starts to show a damping vibration with a time decay constant τ and the thermal depth Ethe of a trapped electron is converted to the lattice vibrational energy [3, 4]. It has been pointed that if the lattice relaxation energy ELR is large, the induced transient lattice vibration may enhance the next majority hole capture. That is, an athermal capture (without activation energy Eacth) of majority hole is possible during the lattice relaxation [5, 6]. If it occurs, the hole capture will induce transient lattice vibration, which will also enhances the next minority electron capture, and so on. In this paper we discuss the possibility of this feedback and inflation mechanism among carrier captures by a deep-level defect and transient induced lattice vibrations using proper configuration coordinate diagrams (CCD) for many carriers, paying attention to the lattice relaxation time τ, the the level position in the gap and ELR. It is found that when both the activation energies Eacte and Eacth are small, a series of successive athermal captures is probable. Even if this feedback mechanism is realized, we find that the possibility of inflation of the lattice vibration
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