Bridgman-grown CuInSe 2 + x with Na or Na 2Se

Abstract

Elemental sodium Na 0 was introduced into Bridgman melts with the two compositions CuInSe 2 (stoichiometric) and CuInSe 2.2 (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 Na 0 content, as found earlier also with Na 2Se additions. Measured thermoelectric power ( α) changed sign from p- to n-type in stoichiometric ingots above 0.1 at.% Na 0, while it remained entirely p-type in ingots with excess Se. However, in earlier work with increasing Na 2Se 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, Cu 3Se 2 and selenium, respectively.