Hexagonal zinc oxide thin films on cubic MgO (100) substrates deposited by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on cubic MgO (100) substrates at different temperatures (100-500 degrees C) using pulsed laser deposition. For comparison, ZnO thin films were also deposited on glass substrates. An x-ray diffractometer was used to investigate the structural properties of the thin films. It was found that the thin films on MgO substrates showed hexagonal structure with (100), (002), and (101) orientations. However, the thin films on amorphous glass substrates show c-axis oriented ZnO only. Spectrometer was used to measure the luminescent properties of the thin films. All of the thin films showed two emission peaks. One was the near band edge (NBE) emission; and the other was the visible deep-level (DL) emission. The thin film on MgO substrate grown at 300 degrees C showed the highest luminescent peak. However, 500 degrees C was found to be the best condition for the thin film grown on glass substrate. The DL emission decreased with time. The thin films were annealed in N-2 and O-2 ambient in a rapid thermal annealing system for 3 min to find the origin of the DL emission. It was found that the oxygen vacancies instead of the zinc interstitials were responsible for the DL emission.