Impurity band characteristics near the band edge of Al-doped ZnO

The characteristics of impurity bands near the band edge of Al-doped and undoped ZnO ceramics were investigated by photoluminescence, photoluminescence excitation, and x-ray diffraction. We found that Al(0.6%)-doped ZnO had two impurity bands whose binding energies were roughly 13 and 99meV below the effective band edge. Also, we found that Al(1.1%)-doped ZnO had an impurity band of ∼80meV binding energy below the effective band edge. As the doping concentration of ZnO increases, Al-impurity bands degenerated from two localized levels to the single localized level. The green band emission of Al(0.6%)-doped ZnO is stronger than those of the pure and Al(1.1%)-doped ZnO because of the high charge transfer rate to the effective band.