Raman spectroscopy of multiphonon emission process in Ni-doped PbTe

Nebojsa Romcevic 1Branka Hadzic 1Jelena Trajic 1Tatyana G. Kuznetsova 2Maja Romcevic 1Zorica Lazarevic 1Dusanka Stojanovic 1Dmitry R. Khokhlov 2

1. Institute of Physics (IF), Pregrevica 118, Belgrade 11080, Serbia
2. M.V. Lomonosov Moscow State University, Vorobyevy gory, Moscow 119992, Russian Federation

Abstract

The doping of AIVBVI semiconducting compounds with transition metal impurities has significant scientific and practical interest. Lead telluride (PbTe) belongs to the AIVBVI IR-sensitive narrow-gap semiconductors group, which acquire new properties in consequence of doping. Transition metals behave either as donors (Cr, Co, Ni) or neutrals (Mn).

In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the samples used here were 1·1019 at.%./cm3. Well resolved peaks appear at about 126, 143, 181, 362 and 724 cm-1. The modes at 126 and 143 cm-1, which are also observed in other telluride compounds, originate from vibrations in TeO2. We assume that the mode at about 181 cm-1 is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor Ni3+ state). Modes at about 362 cm-1 and 724 cm-1 are the second and forth harmonic of a local phonon mode, registered here according to multiphonon emmission (MPE). Namely, in the PbTe(Ni), the equilibrium position of the ground donor level before the electron capture is in the upper half of the gap. After the capture of the electron, the lattice near the defect relaxes in such a way as to lower the equilibrium position of the level in the energy gap. Immediately after the capture of the electron the lattice is displaced far from the new equilibrium position and there will be a violent lattice vibration at the defect. The vibration will rapidly damp down to the amplitude of the thermal vibrations (ω0) after a small number of vibrational periods. During the damping, the localized energy propagates away from the defects as phonons.

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Presentation: Poster at E-MRS Fall Meeting 2008, Symposium A, by Jelena Trajic
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-09 10:14
Revised:   2009-06-07 00:48
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