Characteristics of cobalt-doped zinc oxide thin films prepared by pulsed laser deposition

We have characterized Zn1-xCoxO thin films grown on sapphire (0001) substrates by pulsed laser deposition. We have found for x = 0.25 that inhomogeneous Zn1-xCoxO films with wurtzite ZnO phase mixed with rock-salt CoO and hexagonal Co phases are formed when the growth temperature (T-g) is relatively high (greater than or similar to600 degreesC) and the O-2 pressure (Po-2) is fairly low (less than or similar to10(-5) torr). The presence of the Co clusters leads to room temperature ferromagnetism. Homogeneous Zn1-xCoxO alloy films with wartzite structure are predominantly paramagnetic. High-quality epitaxial Zn1-xCoxO alloy Elms are formed at a growth condition of T-g = 600 degreesC and P-O2 = 10(-5) torr. Under this optimized growth condition, Co can be dissolved into ZnO up to around 40%. Photoluminescence spectra and electrical properties of Zn1-xCoxO strongly depend on the Co content.