Broadband optical response of layered TlGaSe(Formula presented) (Formula presented)from the near-infrared to the ultraviolet: pseudo-optical parameters and vibrational properties
Physica Scripta, vol.101, no.38, 2026 (SCI-Expanded, Scopus)
- Publication Type: Article / Article
- Volume: 101 Issue: 38
- Publication Date: 2026
- Doi Number: 10.1088/1402-4896/aea65b
- Journal Name: Physica Scripta
- Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Compendex, INSPEC, zbMATH
- Keywords: band gap, layered semiconductor, optoelectronic materials, pseudo-optical constants, Raman scattering, spectroscopic ellipsometry, TlGaSe2
- Open Archive Collection: AVESIS Open Access Collection
- Middle East Technical University Affiliated: Yes
Abstract
The broadband optical response of layered TlGaSe (Formula presented) (Formula presented) single crystals was investigated at room temperature by spectroscopic ellipsometry over the photon-energy range of 1.2–6.1 eV, extending from the near-infrared to the ultraviolet. The measured ellipsometric parameters were analysed using a two-phase air/crystal model to derive the effective complex refractive index, dielectric function, absorption coefficient, optical conductivity, and the volume and surface energy-loss functions. All derived quantities are reported as pseudo-optical parameters due to the optical anisotropy of monoclinic TlGaSe (Formula presented) (Formula presented) and the isotropic two-phase model employed. The resulting spectra reveal pronounced dispersion and absorption features associated with the fundamental absorption edge and higher-energy interband transitions. The fundamental absorption onset was located at approximately 2.02 eV from the first derivative of the pseudo-absorption coefficient and is consistent with independently determined band-gap values from transmission and reflection measurements. The below-edge pseudo-refractive-index dispersion was described by the Wemple–DiDomenico single-oscillator model, yielding physically consistent oscillator and static optical parameters. Complementary Raman measurements under two excitation wavelengths confirmed the characteristic intralayer vibrational modes at (Formula presented) (Formula presented) 131, (Formula presented) (Formula presented) 192, and (Formula presented) (Formula presented) 276 cm (Formula presented) (Formula presented). The results establish a self-consistent broadband optical dataset for TlGaSe (Formula presented) (Formula presented) .