Zinc oxide (ZnO) is widely used in various applications such as ultraviolet resistive coatings, gas sensors, sonar for locating fish, and mobile phones. Recently, The transition metal doped ZnO thin films are actively studied due to their potential ferromagnetic properties. The V, Cr, Fe, Co and Ni doped ZnO films were reported theoretically to show a ferromagnetic with a high curie temperature above 300K. Among the above dopants, Cr doped ZnO was prepared by pulse laser deposition and showed no indication of ferromagnetism. The co-doping of Li into ZnO:Cr, however, was reported to show a ferromagnetic phase by using sol-gel method. In this paper, we have therefore reported on the influence of Cr contents on MBE method.
ZnO epilayers were grown on (1120) oriented sapphire substrates by RS-MBE. After the thermal cleaning of the sapphire substrate for 20min at 750oC, the LT-ZnO buffer layer was grown at 250oC, and then annealed at 750oC for 30min to improve the crystalline quality and surface smoothness. Cr doped ZnO layers were grown on the ZnO buffer layers at the temperature range of 400oC to 700oC. The epilayers during annealing and growth were characterized by using in-situ RHEED observation. After growth, the Cr doped ZnO layers were studied by XRD and ESR measurements.
A sharp streaky RHEED pattern was observed throughout non-doped ZnO growth, however the RHEED patterns changed from streaky to spotty patterns with increasing growth time, and then the patterns became spotty after 3hours growth from [1-100] and [2-1-10] azimuths. As from XRD analysis, the FWHM of XRD on Cr doped ZnO became larger with Cr-Cell temperature. These show that irradiated Cr atoms disturb the migration of atoms on the growth surface and degenerate the crystallinity of Cr doped ZnO layer. Finally, we measured the Cr atom related ESR signal from Cr doped ZnO layer on 300K.
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