Carrier polarity reversal with sodium addition in Bridgman-grown CuInSe2

Ingots containing monocrystals of CuInSe2, grown in this laboratory from stoichiometric melts by a one-ampoule Bridgman method, have always been found to be p-type but become n-type if 0.3 at.% or more of elemental sodium is added to the pre-growth melt. However, if excess selenium is present in the melt, corresponding to the formula CuInSe2 + x, with x = 0.2 or 0.4, the ingots remain p-type with sodium additions up to 3 at.% at least. Even so, with smaller Se excesses of x = 0.005, 0.02 and 0.05, conversion from p- to n-type has been observed in the material with sufficient sodium additions. From the results, a relationship between x and the amount of sodium required for type conversion is beginning to emerge.