On the Characteristics of Zinc Oxide Films Grown on (11-20) Sapphire Substrates by Atomic Layer Deposition Using Diethylzinc and Nitrous Oxide

Zinc oxide (ZnO) films were grown on (11-20) sapphire substrates at 600oC by atomic layer deposition (ALD) using diethylzinc (DEZn) and nitrous oxide (N2O). For a typical growth run, a ZnO buffer layer was deposited at low temperature (LT) prior to the growth of a bulk ZnO film. In some cases, buffer-layer annealing or post-annealing treatments were employed to optimize ZnO growth. Based on the experimental results of x-ray diffractometry (XRD) and transmission electron microscopy (TEM), all the as-grown ZnO films were found to show c-axis preferred orientation with co-existence of <1-100>ZnO ||<1-100>sapphire and <11-20>ZnO||<1-100>sapphire relationships in the (0001)ZnO/(11-20)sapphire hetero-interface. Typical room temperature (RT) photoluminescence (PL) spectrum of the as-grown ZnO film shows only near band edge (NBE) emissions without defect luminescence. ZnO films with improved quality were achieved by post-annealing or buffer-layer annealing treatments. In particular, buffer-layer annealing was found to remarkably improve the crystalline and optical properties of a ZnO film.