Well-aligned Cd-Al codoped ZnO nanorod arrays have been synthesized on Ni catalyst-coated p(+)-Si(111) substrates by a chemical vapor deposition technique. It is demonstrated that the obtained codoped ZnO nanorod arrays are single crystallinity with the wurtzite hexagonal phase and preferably grown along the [0001] direction. The optical properties of the nanostructures are characterized by the Raman and photoluminescence techniques. The rectifying characteristics of the p-n heterojunction composed of codoped ZnO nanorod arrays and a p(+) silicon chip are observed. The possible growth process based on VLS mechanism is proposed for the formation of codoped ZnO nanorod arrays. (C) 2009 Published by Elsevier B. V.