Theoretical investigation of electronic structure and thermoelectric properties of CN point defects in GaN

GaN bulk with CN point defects has been theoretically calculated using Density Functional Theory and Boltzmann transport theory. Pure GaN and GaN with two CN of the nearest neighbor, the second-nearest neighbor, and the third-nearest neighbor were carried out to investigate the energy band, density of states, and thermoelectric properties. Compared to pure GaN, it was found that impurity levels appear, which lead to the moving down of the Fermi level and then the moving up of top valence bands in GaN with CN defects. Combining with total density of states (TDOS) and partial density of states (PDOS), we found C(p) makes the main contribution to the moving down of the Fermi level. Then, the highest value of figure-of-merit (ZT) was calculated to be 2.66 of GaN with two CN of the nearest neighbor, while it is only 0.94 of pure GaN at 900 K for p-type. ZT of pure GaN and GaN with CN defects are almost the same at room temperature. In short, impurity levels that appeared in GaN in the energy band were related to CN point defects, which are useful for the improvement of thermoelectric properties on GaN at high temperatures. The research is useful for the application of GaN-based semiconductors.