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 ${\mathit{E}}_1$, ${\mathit{E}}_1$+${\mathrm{\Delta }}_1$, and ${\mathit{E}}_3$ critical-point energies on the temperature is obtained. The structures were analyzed by fitting the second-derivative spectra ${\mathit{d}}^2$ ${\mathrm{\epsilon }}_2$/d${\mathrm{\omega }}^2$ to analytic critical-point line shapes. Satisfactory fittings were obtained using Fano profiles that describe the observed peaks in terms of exciton formation. The ${\mathit{E}}_3$ 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.