OPTICAL AND PHOTOELECTRIC PROPERTIES OF TLGASE2 LAYERED CRYSTALS

Absorption spectra of thin layers of TlGaSe2 crystals are used to study the energy gap and the interband transitions of the compound in the energy region 1.5-3.8 eV and in the temperature range 12-290K. A peak of excitonic origin appears at 2.39 eV at 12K, 0.3 eV above the fundamental direct gap. It is followed by two sharp structures at 2.49 eV and 2.56 eV (12K). A broad structure appears at 2.64 eV. A room temperature reflection spectrum is also presented. The temperature dependence of the critical energies of all the observed structures is given. The dependence of the broadening parameter on temperature and the binding energy of the main exciton peak are also presented. Photoconductivity measurements at 290K and 90K resolve a number of structures that can be identified with several optical transitions. A peak associated with an acceptor level at 0.43 eV above the valence band maximum is also registered.