Birefringence of SnSe single crystals in excitonic and electronic transitions region

Abstract

Absorption spectra in temperature range 300–10 K were studied. The minimal band gap A1 (1.091 eV at 300 K) is formed by direct allowed in E∣∣c polarization and forbidden in E∣∣a polarizations transitions. The next interval B1 (1.316 eV) is formed by direct transitions allowed in E∣∣a polarization and forbidden in E∣∣c polarization. Angular dependences of the electron transitions in the band gap minimum were investigated. Spectral dependences of refractive index (n) were calculated from wavelength modulation transmission (ΔT/Δλ) and reflection (ΔR/Δλ) spectra in the region of direct electron transitions. The absorption edge shifts to higher energies with temperature decreasing, and temperature coefficient of edge absorption shift (β) is 3.4 × 10−3 eV K−1.