Electrical and magnetic properties of oxide-based diluted magnetic semiconductor through rare-earth doping

In recent years, the ability of gadolinium-doped zinc oxide (Gd-doped ZnO) semiconductors to achieve ferromagnetism thin films at room temperature have attracted enormous attention among researchers and scientist due to their potential ideal materials for many applications such as solar cells, sensors, spintronic and etc. A necessary condition to realize towards new-functional devices is to have materials that exhibit ferromagnetism above room temperature. Diluted magnetic semiconductors (DMS) system is where the magnetic ions such as the transition metals and rare earth elements partially substitute the main group cation in wurzite structure. Ever since the discovery of the ferromagnetism in (In, Mn)As and (Ga, Mn)As, researchers have widely studied over other magnetic materials that has potential application towards new-functional devices. Gd rare-earth (RE) atoms have interesting magnetic properties which would induce ferromagnetism behavior with its small amount of doping
concentration into ZnO compared to doping ZnO with the transition metals. However, systematic study on this new type of DMS is still lacking in terms of synthesis and
materials properties in which room for improvement are still wide open in pursuing the suitable material for spintronic device. Therefore, in this research, Gd-doped ZnO
thin films have been synthesized using sol-gel spin-coating technique. Series of experiments have been conducted to investigate the effect of several parameters such as different pre-annealing, post-annealing and hour annealing temperature, Gdcontents (i.e. undoped to 16%) and varying the type of substrates (i.e. glass, aluminium (Al) doped ZnO (AZO), fluorine doped tin oxide (FTO) and silicon (Si)). As a result, the Gd-doped ZnO film with 4% of Gd content exhibits interesting magnetic behavior at room temperature. The properties of Gd-doped ZnO have been investigated using
x-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), atomic force microscopy (AFM), ultra-violet visible spectrophotometer (UV-Vis), photoluminescence (PL), magnetic force microscopy (MFM) and vibrating sample magnetometer (VSM). The XRD analysis shows that the Gd-doped ZnO film is hexagonal wurzite structure and exhibits preferential growth along the (0 0 2) plane. The AFM image shows the surface of the film is homogeneous and uniform. In addition, the UV-Vis analysis indicates the film is highly transparent with average transmission of approximately 90% in the visible region. The MFM images show presence of magnetic domain on the film surface and VSM further confirmed the film is indicating magnetic properties at room temperature. For the four-point probe measurement, it shows that the electrical resistivity of sample on glass substrate is 2.01 x 102 Ω cm and the conductivity is 4.98 x 10-3 S/m. Meanwhile, sample on Si substrate shows higher conductivity of 9.9 S/m and lower resistivity of 1.01 x 10-1. With this
result, it shows that Si substrate is more compatible on fabricating devices.