Characteristics of XPS Se 3d peaks in crystalline Bridgman CuInSe2+x with added sodium in the melt

Using multi-crystalline samples of Bridgman-grown CuInSe2+x, containing added quantities of elemental sodium or Na2Se, detailed XPS measurements were made to determine the location and action of the sodium. Here, the XPS peaks Se 3d, Na 1s and O 1s were given special attention. In particular, two main 3d peaks were observed at binding energies of 54.5 and 59 eV. The first of these, previously assigned mainly to the basic CuInSe2 compound, increased with argon etching time, starting from the ingot surface, but was little affected by the presence of the Na. However, the second peak only appeared when Na or Na2Se had been previously added to the melt. The intensity of this 59 eV peak increased with that of the Na 1s peak at 1071 eV at the surface and with the atomic percentage of the Na added to the Bridgman melt. It also increased somewhat with the amount of contaminant oxygen present in the ingots. The 59 eV peak was thus tentatively assigned to Na2SeO3 resulting from the air-oxidation of Na2Se.