Higher interband transitions in the uv region of GaSe.

Abstract

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 ${\mathit{E}}_{1}$, ${\mathit{E}}_{1}$+${\mathrm{\ensuremath{\Delta}}}_{1}$, 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{\ensuremath{\epsilon}}}_{2}$/d${\mathrm{\ensuremath{\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.