Ion implantation experiments of indium (In) into sputter-deposited undoped ZnO films were carried out to control the resistivity for n(+)-ZnO layers of electronic device. Improvement of ZnO crystallinity after the ion implantation was revealed by x-ray diffraction patterns including a shift of lattice parameter, enhancement of peak intensity, and a decrease in full width at half maximum in 2 theta. In-implanted ZnO crystallinity was greatly improved compared to results of the Ga and Al-implanted ZnO experiments. The resistivity of 1 x 10(16) ions/cm(2) implanted ZnO film was decreased with over 11 orders of magnitude to 5.1 x 10(-2) Omega cm with postimplantation annealing at 400 degrees C. The ratio of resistivity between unimplanted ZnO and In-implanted one at 1 x 10(15) ions/cm(2) was seven orders of magnitude after annealing at 300 degrees C. The In-implanted ZnO would be suitable for fabricating source and drain regions of ZnO thin film transistors. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3259843]