The Study On Structure And Properties Of Cu-ZnO Films

As a directly wide band gap semiconguctor, ZnO film is a well-known material with a hexagonal crystalline stracture, wide band gap (3.37eV) and large excitonic binding energy (about 60meV). The characteristics of ZnO films can be used in solar cells, piezoelectric device, optoelectric device, and gas sensors so on. Recently, the studies for diluted magnetic semiconductors (DMS) have now attracted much attention of many researchers, which exploits spin in magnetic materials along with the charge of electrons in semiconductors. It has been found that the DMS formed by replacing the cations of IV-VI, II-VI or III-V nonmagnetic semiconductors by transition Fe, Mn, Co and Cr can exhibit a number of unique magnetic, magneto-optical, and magnetotransport properties, applicable for magnetoelectronic and spintronic devices. Specially, based on mean field theory, ZnO is a promising candidate for producing a DMS with a Curie temperature above room temperature. Some groups have done great efforts on the study for ZnO based DMS and gotten a series of research results.In this paper, Zn_1-xCu_xO films were prepared by the radio-frequency magnetron sputtering technique on Si substrates and quartz glasses, then we discuss the influence of Cu-doped on the structure, optical, electronic and magnetic properties of ZnO films. In our experiment, the sputtering was performed with Ar gas and pure ZnO target (99.99%). For doping Cu, we adhibited some pieces of Cu on the ZnO target and used co-sputtering method to prepare Zn_1-xCu_xO films.XRD and SEM results indicate that ZnO films doped with moderate Cu dopant (x=0.05) can obtain good wurtzite structure with nanorods aligned perpendicularly to the substrate surface, but the structure of films become badly with more Cu-doped. Raman spectra of films show prominent mode representative of structural defects such as oxygen vacancies and Zn interstitials.From the PL spectrum of the Zn_1-xCu_xO films, we found three PL peaks at 418nm, 440nm and 500nm, respectly. And the PL peaks decreased with increasing Cu concentration. We thought that the peaks we found in PL spectrum may be due to the defects of films.RT ferromagnetism was observed in these films and saturation magnetic moment decreases with Cu concentration increasing. On addressing of the origin of ferromagnetism in the films, the electrical resistance of corresponding films was measured. The insulating nature of films rules out free-carrier mediated mechanism, which is used to explain the observed FM in DMS by some group. Based on the above analysis, the origin of ferromagnetism for these insulating films could be explained by BMP model.