Temperature-dependent optical properties of PtSe₂ thin films with semiconducting-semimetal transitions

Desman Perdamaian Gulo^1*, Han Yeh², Wen-Hao Chang², Hsiang-Lin Liu¹

¹Physics, National Taiwan Normal University, Taipei City, Taiwan
²Electrophysics, National Chiao Tung University, Hsinchu, Taiwan

* Presenter:Desman Perdamaian Gulo, email:desmanpg91@gmail.com

PtSe₂ is promising for use in next-generation sensor, optoelectronics, and ultrafast photonic devices. However, most of optical measurements have been limited at room temperature. Here, we systematically investigated the optical properties of bilayer and multilayer PtSe₂ thin films through spectroscopic ellipsometry over a spectral range of 0.73–6.42 eV and at temperatures between 4.5 and 500 K. We found that the thermo-optic coefficients of bilayer and multilayer PtSe₂ thin films were (4.31 ± 0.04) ☓ 10-⁴/K and (–9.20 ± 0.03) ☓ 10-⁴/K at a wavelength of 1200 nm. The optical absorption spectrum at room temperature confirmed that bilayer PtSe₂ thin films had an indirect band gap of approximately 0.75 ± 0.01 eV, whereas multilayer PtSe₂ thin films exhibited semimetal behavior. The band gap of bilayer PtSe₂ thin films increased to 0.83 ± 0.01 eV at 4.5 K because of the suppression of electron-phonon interactions. Furthermore, the frequency shifts of Raman-active Eg and A1g phonon modes of both thin films in the temperature range between 10 and 500 K accorded with the predictions of the anharmonic model. These results are useful for the technological development of PtSe₂-based optoelectronic and photonic devices at various temperatures.

Keywords: PtSe2, temperature-dependent, spectroscopic ellipsometry, Raman scattering