Urbach tail and bandgap analysis in near stoichiometric LiNbO3 crystals

• Published in: Physica status solidi. A, Applications and materials science Vol. 209; no. 1; pp. 176 - 180
• Main Authors: Bhatt, R., Bhaumik, I., Ganesamoorthy, S., Karnal, A. K., Swami, M. K., Patel, H. S., Gupta, P. K.
• Format: Journal Article
• Language: English
• Published: Berlin WILEY-VCH Verlag 01-01-2012; WILEY‐VCH Verlag; Wiley-VCH
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; LiNbO3 crystals; Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity; optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Physics; Raman scattering; Urbach energy; Optical phonons; Raman spectra; Energy gap; Phonon mode; Lithium niobates; Urbach rule; Absorption spectra; Allowed transition
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.201127361

Energy of the indirect and direct optical bandgap of near‐stoichiometric lithium niobate (nSLN) crystals is evaluated by optical absorption measurement. The value of the indirect bandgap (3.95 eV) is consistent with the earlier reports. However, the direct bandgap energy of 4.12 eV is higher than the previously reported experimental value (3.68 eV). The direct bandgap energy obtained here is closer to the recent theoretical value estimated by Thierfelder et al. [Phys. Status Solidi C 7, 362 (2010)] in comparison to the previously predicted value by Ching et al. [Phys. Rev. B 50, 1992 (1994)]. The phonons involved in the indirect allowed transitions have energies ∼85 meV (685 cm−1) and are identified as the E(TO9) and E(LO8) optical phonon modes from the Raman scattering measurement.