P- to n-type conversion with sodium addition in bridgman-grown CuInSe2

Ingots containing monocrystals of CuInSe₂ have been fabricated, using a Bridgman-growth procedure, in quartz ampoules, to which varying concentrations of sodium and excess selenium have been added. The CuInSe₂ ingots were nominally p-type, but could be made n-type by adding sufficient sodium to the melts before growth. Small additions of excess Se required that greater additions of Na be introduced for the type conversion to occur. The occurrence of deposits found within the ampoules after growth was strongly indicative of conductivity type. Hall coefficient measurements were carried out on some samples, as were compositional analyses by SEM/EDX, revealing the grown material to be deficient in Cu, regardless of type. Additionally, analysis of the interior of an ingot uncovered no Na within the bulk material, but a significant quantity was found on the exterior surface. This marks the first time sodium was shown to reside only on surfaces, rather than within the bulk crystals, in melt-grown material where sodium was added before compound synthesis.