Investigations of sodium in bridgman-grown CuInSe2

Measurements of thermoelectric power (¿) and electrical resistivity (¿) were made at room temperature on filamentary samples of CuInSe² (stoichiometric) and CuInSe_2.2 (excess Se), Bridgman-grown with added elemental sodium in the melt in the amounts of 0, 0.1, 0.2, 0.5, 1, 2 and 3 at. %. In the CuInSe₂ + Na samples, conversion from p- to n-type occurred between 0.2 and 0.5 at. % Na, yielding electron concentrations of the order of 10¹⁶ cm^-3. By contrast, the CuInSe_2.2 + Na samples remained p-type at all the sodium addition levels, yielding hole concentrations of the order of 10¹⁸ cm^-3. In the important range 0 to 0.5 at. % Na, where sample brittleness is less of a problem than for higher additions, no major changes occurred in hole mobility or resistivity but a small increase in ¿_p and a small decrease in ¿ was apparent at 0.1 at. % Na.