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 A 1 (1.091 eV at 300 K) is formed by direct allowed in Emidmidc polarization and forbidden in Emidmida polarizations transitions. The next interval B 1 (1.316 eV) is formed by direct transitions allowed in Emidmida polarization and forbidden in Emidmidc 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.