Surface Stabilities of Various Crystal Faces of CuInSe₂ and Related Compounds by First-Principles Calculation

The typical crystal surfaces of CuInSe₂ (CISe) and related compounds were studied using density functional theory (DFT) methods. We evaluated energies and surface structures of (112), (), (110), (102), (100), (00), (001), and (00) surfaces on CISe. For CISe, the (112) surface had the lowest energy among these surfaces, and the (110) and (102) surfaces had slightly higher energies than the (112) surface. These surface atoms coordinate with the three surrounding atoms. We found that the (112) surface is most stable for CISe, and this result is consistent with the experimental results showing that the (112) surface is most frequently observed in polycrystalline CISe thin films. We also evaluated the surface energies of CuGaSe₂ (CGSe), CuAlSe₂ (CASe), CuInS₂ (CIS), CuInTe₂ (CIT), and AgInSe₂ (AISe). For CGSe, CIS, and CIT, the (112) surface had the lowest energy as in the case of CISe. However, for CASe and AISe, the (110) surface had the lowest energy.