Thermoelectric properties and microstructure of Cu-In-O thin films

Combinatorial chemistry techniques were used to study the thermoelectric properties of sputtered thin films in the system copper oxide (CuO) and indium oxide (In2O3). Seven hundred seventy thin film thermocouples or combinatorial library elements were simultaneously deposited, each with a unique spatially dependent chemistry, based on the relative position of the thermocouples to each sputtering target. The resulting thermoelectric properties of each element were determined along with electrical resistivity as a function of composition. Energy dispersive spectroscopy was used to identify the composition of each thermo-element, and electron and X-ray diffraction were used to determine the degree of crystallinity and phases present. Transmission electron microscopy was used to characterize the microstructure of selected thermo-elements. A change in sign of the thermoelectric voltage was observed in the thermo-element containing 40.0 atomic percent indium, which suggests a change in the dominant carrier type occurred, from p-type to n-type. Based on this finding, the fabrication of thermoelectric p-n junctions using the same base Cu-In-O semiconductor appears feasible.