Absorption and electro-absorption in single-crystal As₂Se₃near the fundamental edge

Optical absorption and electro-absorption spectra are reported for single crystals of As 2 Se 3 extending to low values of alpha ( approximately 1cm -1 ). The authors observe a well defined Urbach tail above approximately 100K and phonon thresholds at 4-40K. The electro-absorption spectra show a marked temperature- and field-broadening. An analysis is given in terms of indirect excitons.