Temperature-dependent indirect gaps for two-dimensional bismuth oxychalcogenides probed by spectroscopic ellipsometry
Journal
2D Materials
Journal Volume
11
Journal Issue
3
Start Page
035029
ISSN
20531583
Date Issued
2024
Author(s)
Liu, Hsianglin
Chen, Hsiaowen
Chen, Yicheng
Liu, Hengjui
Chen, Chiehting
Chueh, Yu Lun
Chu, Yinghao
Saito, Riichiro
Abstract
In-plane optical properties of two-dimensional bismuth oxychalcogenides Bi2O2X (X = S, Se, and Te) are reported for a wide spectral range of 0.73-6.42 eV and at temperatures of 4.5-500 K by spectroscopic ellipsometry. At room temperature, Bi2O2S, Bi2O2Se, and Bi2O2Te exhibit an indirect band gap of 1.18 ± 0.02, 0.95 ± 0.01, and 0.60 ± 0.01 eV, respectively. As the temperature decreases, the indirect absorption edge of Bi2O2S undergoes a blueshift, while the indirect band gap of Bi2O2Se shows a redshift, and Bi2O2Te remains independent of temperature. The chalcogenide-dependent behavior as a function of temperature may be relevant to electron-phonon interactions in Bi2O2X materials. The observed pseudo-isotropic complex dielectric function and optical absorption coefficient by spectroscopic ellipsometry are directly compared with the first-principles calculations with a hybrid functional approach.
Subjects
First-principles Calculations
Spectroscopic Ellipsometry
Two-dimensional Bismuth Oxychalcogenides
Absorption Spectroscopy
Electron-phonon Interactions
Energy Gap
Layered Semiconductors
Light Absorption
Selenium Compounds
Spectroscopic Ellipsometry
Tellurium Compounds
Absorption Edges
Blue Shift
First Principle Calculations
Indirect Band Gap
Oxychalcogenides
Temperature Decrease
Temperature Dependent
Two-dimensional
Two-dimensional Bismuth Oxychalcogenides
Wide Spectral Range
Bismuth Compounds
Publisher
Institute of Physics
Type
journal article