Bridgman-grown CuInSe2 with added Na2Se and Na

Ingots containing single crystals were grown from melts containing Cu, In and Se in either stoichiometric proportions (CuInSe2) or with an excess of Se (CuInSe2.2). In addition, elemental sodium Na⁰ was introduced to both sets of compositions in concentrations ranging from 0 to 3 at. %. Analysis of white deposits on the ampoule walls after growth revealed the presence of Na, however, none was found within the crystals. Further, a red deposit was also analyzed, and was revealed to contain sodium and various forms of the other elements. Thermoelectric power (α) measurements showed little change in the p-type conductivity of CuInSe2.2 ingots with increases of Na⁰, but a dramatic type change from p to n was observed for stoichiometric CuInSe2 with Na⁰ concentrations above at least 0.1 at. %. This is in stark contrast to previous work using Na2Se, for which α was seen to decrease for both CuInSe2 and CuInSe2.2, implying a hole concentration increase of more than an order of magnitude.