Investigation of the Optimal Annealing Temperature for the Enhanced Thermoelectric Properties of MOCVD-Grown ZnO Films

In this study, we demonstrate the optimization of the annealing temperature for enhanced thermoelectric properties of ZnO. Thin films of ZnO are grown on a sapphire substrate using the metal organic chemical Vapor Deposition (MOCVD) technique. The grown films are annealed in an oxygen environment at 600-1000 degrees C, with a step of 100 degrees C for one hour. Seebeck measurements at room temperature revealed that the Seebeck coefficient of the sample that was not annealed was 152 mu V/K, having a carrier concentration of N-D similar to 1.46 x 10(18) cm(-3). The Seebeck coefficient of the annealed films increased from 212 to 415 mu V/K up to 900 degrees C and then decreased at 1000 degrees C. The power factor is calculated and found to have an increasing trend with the annealing temperature. This observation is explained by the theory of Johnson and Lark-Horovitz that thermoelectric properties are enhanced by improving the structure of ZnO thin films. The Hall measurements and PL data strongly justify the proposed argument.