Optical absorption measurements in the wavelength range 1.3-1.6 microns in Bridgman CuInSe2 grown from melts with added sodium

Measurements of optical absorption coefficient (α) were made on Bridgman-grown CuInSe₂ samples, over the wavelength range 1300 to 1600 nm, at room temperature. The samples were obtained from multi-crystalline ingots, grown from melts of composition CuInSe_2+x, plus y atomic % of elemental sodium. Here, x, the excess of Se over stoichiometry, ranged from 0 to 0.4 and y, the percentage of Na in the melt, ranged from 0 to 11 at %. It was found that α was considerably increased by the original Na in the melt and also by a stoichiometric deficiency of Se in the melt; that is with a melt formula corresponding to CuInSe_1.8, (or x = - 0.2). A smaller increase of α was observed with increase of x, the Se excess. With the addition of Na₂Se in the melt, little change was obtained compared with the large increase with elemental Na.