Above-bandgap ordinary optical properties of GaSe single crystal

We report above-bandgap ordinary optical properties of ε-phase GaSe single crystal. Reference-quality pseudodielectric function ⟨ε(E)⟩=⟨ε1(E)⟩+i⟨ε2(E)⟩ and pseudorefractive index ⟨N(E)⟩=⟨n(E)⟩+i⟨k(E)⟩ spectra were measured by spectroscopic ellipsometry from 0.73to6.45eV at room temperature for the light polarization perpendicular to the optic axis (E⃑⊥ĉ). The ⟨ε⟩ spectrum exhibited several interband-transition critical-point structures. Analysis of second-energy derivatives calculated numerically from the measured data yielded the critical-point energy values.