Electrical and magnetic properties of (In, Co) co-doped ZnO films deposited using radio frequency magnetron sputtering

Diluted magnetic semiconductors (DMSs) have attracted much attention in recent years due to their dual control of charge and spin degrees of freedom in carriers. Potential applications of DMSs include spin light-emitting diodes, spin field-effect transistors, magnetoresistance random access memory, and ultrafast optical switches. However, the Curie temperature (Tc) of most DMSs below ambient temperature limits the efficiency of these devices. Thus, the biggest challenge for developing DMS materials has been producing host materials that exhibit ferromagnetic behavior above ambient temperature. A series of theoretical simulations and experiments show that the Tc value of ZnO-based DMSs could satisfy this requirement. Incorporation of selective transition metal elements (e.g., Fe²⁺, Co²⁺, Ni²⁺, and Mn²⁺) has been confirmed as an effective way to enhance the magnetic properties of ZnO. In the present research, (In, Co) co-doped ZnO (ICZO) films were deposited by radio frequency sputtering at 100 ℃ on a glass substrate. The sputtering process was performed through In, Co, and ZnO co-sputtering. The presence of ICZO films has been adjusted by changing the target sputtering power. The variation of electric and magnetic properties of the film was studied with different In content. The composition, morphology, structure, electric and magnetic properties of films were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, electron probe microanalyzer, X-ray diffractometer, Hall effect analysis, and vibrating sample magnetometer. The effect of carrier concentration on the magnetic properties of the film was analyzed extensively. These results show that, in the presence of In, the carrier concentration increases, thereby optimizing films’ conductivity. All the films present ferromagnetic behavior at room temperature. Besides, with an influence of bound magnetic polaron model and carrier-mediated exchange mechanisms on the film’s saturation magnetization, carrier-concentration dependent behavior can be expressed in three different regions.