Effect of thickness on structural, electrical, and optical properties of ZnO: Al films deposited by pulsed laser deposition

To evaluate the influence of thickness on structural, electrical, and optical properties of ZnO:Al (AZO) films, a set of polycrystalline AZO samples with different thicknesses were deposited by pulsed laser deposition. X-ray diffraction measurement shows that the crystal quality of AZO films was improved with the increase of film thickness. Film surface morphology reveals that a transition of growth mode from vertical growth to lateral growth exists when the films become thicker. The resistivity decrease of AZO films with increase of film thickness owes to the change of carrier concentration for < 50 nm thick films, and mainly attributes to the raise of Hall mobility when films are thicker. It is found that the optical band gap increases from 3.58 to 3.90 eV when AZO film thickness increases from 15 to 580 nm , however, the optical transmittance of most AZO films is > 80 % regardless of film thickness in the visible region. The photoluminescence spectra of AZO films can be fitted well by seven emissions, and the emission around 2.82 eV can be assigned to N-deep-level related recombination.