Abstract
The structural and optical properties of ZnO and Zn0.9Al0.1O (AlZnO) samples annealed in air at different temperatures of (400-900 degrees C) for 12 h are investigated. It is found that cell parameters, average crystalline diameter and average grain size are affected by both Al and annealing. The ultra violet (UV) absorption coefficient (alpha) is increased by Al and can be represented by the relation ;(alpha (AlZnO)2 alpha (ZnO), but it is generally decreased by annealing. Two different types of band gap are obtained for each sample in which their values are higher for AlZnO than that of ZnO. The first band gap is called fundamental energy gap (E-gh) and its value above 3 eV, while the second is called optical energy gap (E-gL) and its value below 2.75 eV. In addition, the values of E-gL (ZnO), E-gh (AlZnO) and E-gL (AlZnO) are increased by annealing up to 700 degrees C, followed by a decrease at 900 degrees C, while the values of E-gh (ZnO) are increased by annealing up to 900 degrees C. Furthermore, a unique energy gap of 3.33 eV is obtained at 312 degrees C for ZnO and AlZnO. On the other hand, the lattice dielectric constant (epsilon(L)), free carrier concentration (N/m*), dielectric loss (tan delta), optical conductivity (sigma(opt)) and electrical conductivity (sigma(ele)) are obtained for both series. It is found that epsilon(L) is increased by annealing up to 900 degrees C for both series, while (N/m*) is increased by annealing for ZnO, but it is decreased for AlZnO. But their values are higher for ZnO than that of AlZnO. Further, the value of epsilon(L) (11.26) of the as-prepared ZnO is nearly similar to the value of epsilon(L) (11.76) for AlZnO at 900 degrees C. Although tan delta is similar for both series, it is decreased by annealing up to 900 degrees C for ZnO, and increased for AlZnO up to 700 degrees C followed by decrease at 900 degrees C. Similar behavior is obtained for sigma(opt), while the vice is versa for sigma(ele). The obtained results are interpreted in terms of the variance of carrier concentration, oxygen vacancies and interatomic spacing against annealing temperature and Al content. The present results confirm the semiconducting nature as well as assure that the high photo-response of the investigated samples.