Raman spectroscopy study of compositional inhomogeneity in lithium tantalate crystals
Publication date
2009-04
Document type
Research article
Author
Organisational unit
Technische Universität Clausthal
Scopus ID
ISSN
Series or journal
Applied Physics B Lasers and optics
Periodical volume
95
First page
125
Last page
130
Part of the university bibliography
Nein
Abstract
Raman spectra of LiTaO3 single crystals with various stoichiometries were measured to investigate the compositional uniformity of these crystals. Raman spectra mapping demonstrates a spatial variation of the widths of the phonon bands for stoichiometric, congruent, and quasi-congruent samples. A significant radial compositional inhomogeneity is found to be a common feature of commercially available wafers having a near-congruent crystal composition (i.e., x c ={[Li2O]/([Li2O] +[Ta2O5])}×100%=47.85-48.50%) grown by the single-crucible Czochralski method. A maximum value of the composition gradient x c for a radial inhomogeneity of 0.163 and 0.036%/cm is measured for thin wafers diced from so-called congruent (vendors' value of Δx c =48.50%) and quasi-congruent (x c =47.88%) crystals, respectively. In crystals grown from highly Li-rich melts (starting composition 54.5 mol% Li2O), a drastic spatial dependence of Raman bandwidths, indicating a significant gradual compositional inhomogeneity throughout the crystal, is found, which is due to a change of the melt composition during crystal growth. In contrast, the Raman bandwidths of near-stoichiometric crystals fabricated by a vapor transport equilibrium (VTE) technique are found to be constant, i.e. these crystals are practically compositionally uniform. This conclusion has been confirmed by mapping the photoluminescence intensity, evidencing Δ x c≤0.006%/cm in near-stoichiometric VTE-treated crystals. © 2009 Springer-Verlag.
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