Excitoic Recombination at a Transititon-Metal Related Defect in Silicon
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EXCITONIC RECOMBINATION AT A TRANSITION-METAL RELATED DEFECT IN SILICON K.G. MCGUIGAN*, M.O. HENRY*, E.C. LIGHTOWLERS**, M.H. NAZAR0# * School of Physical Sciences, Dublin City Univeristy, Collins Avenue, Dublin 9, Ireland ** Physics Department, King's College London, Strand, London, WC2R 2LS, UK # Departamento e Centro de Fisica, Universidade de Aveiro, 3800 Aveiro, Portugal ABSTRACT A new photoluminescence system is reported for copper-doped silicon. The luminescence system consists of two doublet zero phonon lines at 1033.51t.05 meV, 1033.62t.05 meV, 1040.05-.05 meV and 1040.l7-.05 meV. We establish from Zeeman studies that the lower energy lines are isotropic magnetic triplets, and the upper energy lines are singlets. From temperature dependence measurements the energy separation between triplet and singlet states is determined to be approximately 6 meV, in agreement with the spectroscopic separation. Also from temperature dependence PL we show that the transition probability ratio for the higher and lower states is 210. We conclude that the main features of the luminescence agree with radiative recombination of excitons bound to an axial isoelectronic defect. The chemical identity of the constituent(s) involved is uncertain although the participation of copper is likely. INTRODUCTION Transition metal elements, even in very low concentrations, are feared contaminants in most semiconductor fabrication processes since they can drastically influence the free-carrier lifetimes and electrical conductivity of the host material [1]. Transition metals are fast diffusers in silicon, in particular copper has a diffusion coefficient of 10-4 cm2 sec at 11000 C [2]. Copper contamination is therefore a frequent occurrence especially after furnace anneals since it is given off by the furnace windings at high temperatures [3]. Over the last ten years several copper related defects have been reported [4,5]. In this paper we report a new band present in the photoluminescence spectrum of copper doped silicon (Figures 1, 2). This luminescence system, labelled SK has doublet zero phonon lines at 1033.51 meV and 1033.62 meV 3 0 (SK and SKi respectively) and at 1040.05 meV and 1040.17 meV (SK and SK4 respectively). We identify this system with the decay of bound excitons at an isoelectronic defect. From Zeeman measurements the higher energy lines are identified as transitions from singlet states (S = 0) and the lower energy lines as transitions from isotropic (S = 1) triplet states. From the temperature dependent behaviour of the zero phonon lines, the transition probability ratio of the triplet and singlet states is found to be about 210, and the energy separation between each triplet-singlet about 6.5 meV in agreement with the spectroscopically observed line separations. EXPERIMENTAL The starting material was an as-received ingot of silicon of 4500 a cm resistivity and with a copper concentration of 1013 atoms cm- 2 measured by atomic absorption. Samples of dimensions 9 x 4 x 2 mm were cut from this ingot, etched to remove any surf
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