Bridgman-grown CuInSe2 + x with Na or Na2Se

Elemental sodium Na0 was introduced into Bridgman melts with the two compositions CuInSe2 (stoichiometric) and CuInSe2.2 (excess Se) in amounts of 0, 0.1, 0.5, 1, 2 and 3 at.%. In the resulting Bridgman-grown ingots brittleness generally increased with increased Na0 content, as found earlier also with Na2Se additions. Measured thermoelectric power (α) changed sign from p- to n-type in stoichiometric ingots above 0.1 at.% Na0, while it remained entirely p-type in ingots with excess Se. However, in earlier work with increasing Na2Se in excess Se ingots, α decreased by about 70%, corresponding to an apparent hole concentration increase of more than an order of magnitude. Four different deposits were observed in the containing ampoules: white and reddish deposits, and grey and black spots. These were found to contain sodium, copper, Cu3Se2 and selenium, respectively.