Higher interband transitions in the uv region of GaSe

Transmission measurements of the layered compound GaSe lead to the determination of the absorption coefficient in the region 3--4 eV and in the temperature range 10--290 K. The dependence of the E₁, E₁+Δ₁, and E₃ critical-point energies on the temperature is obtained. The structures were analyzed by fitting the second-derivative spectra d²{{{ε}}}₂$/d${{{ω}}}²$ to analytic critical-point line shapes. Satisfactory fittings were obtained using Fano profiles that describe the observed peaks in terms of exciton formation. The ${E}₃$ transition is best described by considering a pair of two-dimensional, nearly degenerate critical points. Broadening parameters of the observed critical points and their temperature dependence are also presented.