First-principles study of Si atoms adsorbed on ZnO (0001) surface and the effect on electronic and optical properties

Si atoms adsorbed on ZnO (0001) surface have been investigated by first principles calculations. In the considered Si/ZnO (0001) system, H3-22 is the most stable structure and then is T4-11. The adsorbed Si atoms show many interesting behaviors. For H3-22, the adsorbed Si atoms migrate from two fixed H3 sites to one T4 site and one H3 site. For T4-33 and H3-33, the adsorbed three Si atoms form triangles. For T4-44, one more adsorbed Si atom leads the triangles to change to quadrangle. The triangular or quadrilateral Si structures just belong to S₃ and S₄ clusters. The electronic properties indicate that the absorbed Si atoms decrease the band gaps of the Si/ZnO (0001) system. The width and position of the band gaps are influenced by the adsorption models. From the optical properties analysis of T4-11 and H3-11, it indicates that H3 sites play a critical role in the red shift of absorption edge and T4 sites almost have little contribution. For H3-33, H3-44 and T4-44, the result indicates that the formed Si clusters lead to a slightly blue shift phenomenon and prevent the absorption of sunlight in the lower energy range.