Band structures and optical properties of Ag and Al co-doped ZnO by experimental and theoretic calculation

Abstract

Abstract Crystal structures, band structures, density of states (DOS), optical properties including dielectric function, absorption, loss function, refractive index, reflectivity and photoluminescence (PL) emission are investigated by combining experimental results with theoretic calculation. Results indicated that crystal quality of ZnO is improved after Al and Ag doping. In addition, compared with Al-doped and Ag-doped ZnO, Ag-Al co-doped ZnO have smaller bandgap. It imply that Ag-Al co-doping can adjust the bandgap more flexibly, and then change the electronic structure and optical properties. At the same time, Al-3 p and Ag-5 s states have stronger interaction in Ag-Al co-doped ZnO, which makes the conduction band wider, so the DOS further moves toward lower energy. For Ag-doped ZnO, a very narrow peak at around 0.21 eV is observed in dielectric function spectra, which is associated with the electron transition between Ag-4 d states and partially filled valence band. PL spectra of pure ZnO shows a broad blue emission band at 421 nm, and its intensity increases and the full-width at half maximum (FWHM) decreases after Al and Ag doping. Interestingly, emission band red shifts toward green waveband as Al and Ag is co-doped in ZnO.