Dresden 2006 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 25: POSTER Electronic Structure and Spectroscopy
CPP 25.7: Poster
Thursday, March 30, 2006, 17:00–19:00, P2
Comparison of the Layered Semiconductors GaSe, GaS, and GaSe1−xSx by Raman and Photoluminescence Spectroscopy — •Lothar Kador1, Carmen Pérez León1, Kerim R. Allakhverdiev2, Tarik Baykara2, and Ali A. Kaya2 — 1University of Bayreuth, Institute of Physics and Bayreuther Institut für Makromolekülforschung (BIMF), D–95440 Bayreuth, Germany — 2Marmara Research Centre of TÜBITAK, Materials Institute, P. K. 21, TR–41470 Gebze/Koçaeli, Turkey
The room-temperature Raman spectra of single crystals of GaSe, GaS, and mixed compounds GaSe1−xSx with 0.02 ≤ x ≤ 0.8 were measured with a HeNe laser in confocal configuration. The changes in the spectra indicate changes of the crystal structure. The spectra of pure GaSe and of the mixed compound with x = 0.02 show, in addition, pronounced photoluminescence signals blue-shifted from the laser line. Their origin is interpreted as second-harmonic generation in the laser focus causing the formation and radiative decay of Wannier excitons. Two-photon absorption is ruled out, since the effect is absent in the centrosymmetric crystals with x > 0.02. With a green laser whose photon energy is larger than the band gap, strong photoluminescence is also observed in crystals with higher sulfur content.