Electronic and Optical Properties of Substitutional and Interstitial Si-Doped ZnO

This study investigates the formation energies, electronic structures, and optical properties of pure and Si-doped ZnO using density functional theory and the Hubbard U (DFT + U(d) + U(p)) method. The difference in lattice constants between calculated results and experimental measurements is within 1%, and the calculated band gap of pure ZnO is in excellent agreement with experimental values. This study considers three possible Si-doped ZnO structures including the substitution of Si for Zn (Si(s(Zn))), interstitial Si in an octahedron (Si(i(oct))), and interstitial Si in a tetrahedron (Si(i(tet))). Results show that the formation energy of Si(s(Zn)) defects is the lowest, indicating that Si(s(Zn)) defects are formed more easily than Si(i(oct)) and Si(i(tet)). All three of the Si defect models exhibited n-type conductive characteristics, and except for the Si(i(oct)) mode the optical band gap expanded beyond that of pure ZnO. In both the Si(i(oct)) and Si(i(tet)) models, a heavier effective mass decreased carrier mobility, and deeper donor states significantly decreased transmittance. Therefore, the existence of interestitial Si atoms was bad for the electric and optical properties of ZnO.