We review our recent findings that reactive magnetron sputtering can be operated without thermal assistance to produce epitaxial ZnO films and highly conductive and transparent aluminum-doped ZnO (AZO) films on large surface area. The growth of epitaxial films requires working in direct current (DC) mode at large oxygen partial pressure but high power impulse magnetron sputtering (HiPIMS) is preferred to optimize the electrical and optical properties of AZO films on large surface areas. The results are interpreted by the ability of DC sputtering to easily oxidize the target surface and the HiPIMS mode cleans and returns it to metallic during pulses. Fast oxygen atoms (ions) may be emitted in large amount using DC and bring fuel to the growing ZnO film to induce epitaxy onto sapphire. The signature of oxygen interstitials is found in DC with increasing magnitude as the oxygen content is increased in the gas phase. In contrast, the discharge voltage plays a significant role in HiPIMS to adjust the sputtering rate and clean the target surface for deposition of slightly sub-stoichiometric AZO films over the entire range of lateral positions. Thereby, transparent yet highly conductive films with resistivity in the range 4-15x10(-4) Omega m can be produced. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim