Blue-green emission mechanism and spectral shift of Al-doped ZnO films related to defect levels

The crystal structure, surface morphology, chemical state and optical properties of Al-doped ZnO films grown at different sputtering powers are studied. Results indicated that compressive stress related to defects exists in all the samples measured by X-ray diffraction. Blue-green emission mechanisms and a blue-shift were explored based on defects sites. The peak at 458 nm comes from the electron transition from interstitial Zn to the top of the valence band and transition from the conduction band to misplaced oxygen defects. The peak at 490 nm comes from the electron transition from interstitial Zn to Zn vacancies or interstitial O and transition from a complex defect level of O vacancies and interstitial Zn to the valence band. The existence of compressive stress related to the defects in Al-doped ZnO plays a significant role in the blue-green emission and blue-shift.