Investigating the stability and electronic properties of CuI (111) polar surfaces.

In recent years, CuI has drawn the attention of many researchers as a most suitable p-type transparent conducting material (TCM) due to its large band gap (3.1 eV), large exciton binding energy (62 meV), and high hole mobility (>40 cm² V^-1 s^-1) . Because of these properties, CuI thin films are proposed as prominent candidates for optoelectronics devices such as solar cells, light-emitting diodes, etc. Experimentalists faced some challenges in fabricating the CuI thin films since the orientation and atomic structure of the thin film surface can change the electronic properties. Moreover, it is crucial to understand the surface properties, like, surface reconstruction, surface energy, and band structure for the development of CuI-based devices. Here we investigated the stability and electronic properties of 2x2 reconstructed Cu-terminated and I-terminated polar surfaces using first principles. A standard slab method cannot be used to calculate the surface energies for polar surfaces. Therefore, we used the wedge structure model to evaluate surface energy for one polar surface without involving its associated surfaces. It is been observed that surface with I-termination has the least surface energy among all the reconstructed surfaces. To visualize the electronic properties we have used DensityTool.