The properties of heavily Al-doped ZnO films before and after annealing in the different atmosphere

A radio frequency power (r.f) of 200 W was supplied to ZnO target, and a direct current (d.c.) power of 40 W was supplied to Al target for the preparation of heavily Al-doped ZnO (ZnO:Al) films. The advantage of this kind of deposited method is that the Al content could be changed in a wide range. The ZnO:Al films before and after annealing in N-2 or O-2 all developed a columnar structure. The crystal sizes were nearly the same (approx. 20 nm) for ZnO:Al films before and after annealing in N-2 or O-2. The as-deposited ZnO:Al films had polycrystalline structure and low resistivity (8.52 X 10(-3) Omega cm). After annealing in N-2 or O-2, ZnO:Al films exhibited poor crystallinity, and the resistivity increased substantially. The lower optical energy gap (3.29 eV) could be obtained as ZnO:Al film annealing in O-2. However, the weak absorption in the visible region of the spectrum terminated at shorter wavelengths with the onset of the ultraviolet absorption edge for all samples. Annealing in N-2 or O-2 did not improve the properties of ZnO:Al films. (C) 2004 Elsevier B.V. All rights reserved.