A New Metastable Defect in Silicon, Optical Properties and an Investigation of the Mechanism Causing the Configurational
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A NEW METASTABLE DEFECT IN SILICON, OPTICAL PROPERTIES AND AN INVESTIGATION OF THE MECHANISM CAUSING THE CONFIGURATIONAL CHANGE J. H. SVENSSON, B. MONEMAR Department of Physics and Measurement Technology, Institute of Technology, Link6ping University, S-581 83 Link~ping, Sweden ABSTRACT A new optical transition with a no-phonon energy of 0.615 eV discovered in electron-irradiated silicon grown by the Czochralski technique is investigated, revealing metastable properties of the related defect. The investigation is focused on the optical properties of the transition and its associated structure and on the mechanism governing the change of defect configuration. The transformation of the defect to the metastable state is suggested to be induced by excitonic Auger recombination. A pseudo-donor model is presented as an explanation of the optical spectrum. INTRODUCTION A number of optical no-phonon transitions with varying coupling strength to phonons have been investigated in electron-irradiated silicon grown by the Czochralski-technique. The most prominent of these transitions have no-phonon energies at 0.790, 0.969 and 0.489 eV, respectively [1-6] In the case of the 0.790 eV transition, electronic excited state structure is clearly observed [4]. The excitation structure has been explained as due to electronic excited states of an electron, that in its excited states is bound by the Coulomb field of a tightly bound hole. The electron and the bound hole are
envisioned as a pseudo-donor [5]. The defect causing the no-phonon line at 0.969 eV has been proposed to be an interstitial-substitutional carbon pair; moreover the defect is believed to have two stable geometrical configurations [6]. Transformation between the two configurations was observed when the sample was optically excited with a YAGlaser at temperatures below 50 K. Recently a new no-phonon transition in irradiated silicon was found at 0.615 eV [7]. Additional structure is observable at higher photon energies, approximately 165 meV above the no-phonon line. This line and the structure are only observed when the sample is optically excited at temperatures below 65 K. The entire structure disappears when the sample is heated to temperatures exceeding 70 K [7] and the thermal activation energy for the disappearance is 0.21 eV. A model explaining the results as being caused by a carbon-related defect with two configurations in the neutral charge state was put forward. In the present work we have investigated the kinetics of the growth in intensity of the 0.615 eV no-phonon line using two different optical excitation sources to induce the growth. We also present results from an optical investigation of the absorption structure. EXPERIMENTAL The samples are Czochralski-grown phosphorus-doped silicon crystals, with an initial resistivity of 40 Qcm at room temperature. The samples were polished to Mat. Res. Soc. Symp. Proc. Vol. 163. ' 1990 Materials Research Society
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obtain optical surfaces and then irradiated at room temperature with 2 MeV electrons. After the
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