Ohmic contact formation assisted by metallic states at the interface of Cu2Te/CdTe

Ohmic contact to CdTe is a formidable task, but is indispensable for achieving high-efficiency in CdTe thin film solar cells. Using first-principles calculations within density functional theory, we study the structures and Schottky barrier heights (SBHs) of the widely used Cu$_{2}$Te/CdTe contact interfaces. We obtain two main structural configurations of the Cu$_{2}$Te layers on CdTe(111), with physically reasonable formation energies: epitaxial and bulk-like Cu$_{2}$Te layers. The epitaxial Cu$_{2}$Te layers possess Cu-Te bonds with the CdTe(111) surface, maintaining the hexagonal, unreconstructed CdTe(111) structure. In contrast, for the bulk-like Cu$_{2}$Te layered, both unreconstructed and reconstructed CdTe(111) surfaces are possible due to weak interactions between the Cu$_{2}$Te and CdTe interfaces. Detailed calculations of the SBHs at the Cu$_{2}$Te/CdTe interfaces show that the interfaces with an unreconstructed CdTe(111) surface have a low SBH of \textless 0.24 eV, consistent with our experimental observation of \textless 0.3 eV. These findings may serve as an important guidance in future efforts for improving contact quality of semiconductor devices.