Two - Color Mid-Infrared Spectroscopy of Isoelectronic Centers in Silicon
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Two - Color Mid-Infrared Spectroscopy of Isoelectronic Centers in Silicon
N.Q. Vinh and T. Gregorkiewicz Van der Waals - Zeeman Institute, University of Amsterdam, The Netherlands.
ABSTRACT One of the open questions in semiconductor physics is the origin of the small splittings of the excited states of bound excitons in silicon. A free electron laser as a tunable source of the mid-infrared radiation (MIR) can be used to investigate such splittings of the excited states of optical centers created by transition metal dopants in silicon. In the current study, the photoluminescence from silver and copper doped silicon is investigated by two color spectroscopy in the visible and the MIR. It is shown the PL due recombination of exciton bound to Ag and Cu is quenched upon application of the MIR beam. The time-resolved photoluminescence measurements and the quenching effects of these bands are presented. By scanning the wavelength of the free-electron laser ionization spectra of relevant traps involved in photoluminescence are obtained. The formation and dissociation of the bound excitons, and the small splittings of the effective-mass excited states are discussed. The applied experimental method allows correlation of DLTS data on trapping centers to specific channels of radiative recombination. It can be applied for spectroscopic analysis in materials science of semiconductors.
INTRODUCTION Bound exciton recombination gives sharp luminescence lines in the near band-gap region of most semiconductors. Shallow donors and aceptors as well as isoelectronic impurities are known as exciton binding centers. The binding energy of excitons bond to isoelectronic centers does not follow simple systematics. This is due to a more complicated binding mechanism in these complexes. An electron bound to a positive charge core of a neutral defect experiences two partly overlapping potentials: central-cell potential with a short range interation and the Coulond potential with a long range interaction. The Coulomb potential of the positive charge localized at the core gives rise to hydrogenlike excited states described by the effective-mass approximation (EMA).
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The photoluminescence (PL) of silver-doped silicon has been investigated in the past and in generation of a characteristic low temperature emission spectrum at 780 meV [1-5] has been concluded. In the photoluminescent spectrum, narrow no-phonon lines (termed A, B, and C with energies of 778.9, 779.9 meV and 784.4 meV, respectively) and lower energy phonon replicas have been distinguished. The observed structure was identified as transitions from the effectivemass-like electronic states near the conduction band to the ground state. The PL spectrum of copper-doped silicon has two bands at 1014.7 meV [6] and 943.7 meV [7], each of t
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