OPTICAL-PROPERTIES OF UNDOPED AND CO-DOPED CUGA1-XALXSE2 SINGLE-CRYSTALS

Single crystals of CuGa1-xAlxSe2 and CuGa1-xAlxSe2:Co2+ were grown by the chemical transport reaction (CTR) method using iodine as the transport agent. From optical absorption spectra of these compounds, the composition dependence of the optical energy gap and the origin of the impurity optical absorption due to the cobalt impurity are investigated. The origin of the impurity optical absorption in CuGa1-xAlxSe2:Co2+ single crystals has been analyzed by the static crystal field theory. Co2+ ions in CuGa1-xAlxSe2:Co2+ single crystals are located at the host lattice of CuGa1-xAlxSe2 single crystals with cubic T(d) symmetry. It was observed that the impurity absorption peaks are attributed to the electronic transitions between the split energy levels of Co2+ ions.