GROWTH OF FERROMAGNETIC SEMICONDUCTOR LITHIUM DOPED ZINC OXIDE THIN FILMS USING AA-MOCVD AND MAGNETOTRANSPORT MEASUREMENT

• Main Author: Arief Mustajab E. M., Muhammad
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/85196
• Institution: Institut Teknologi Bandung

d 0 ferromagnetic semiconductor materials have potential as one of spintronic material to avoid the controversy of magnetic metal doping in diluted magnetic semiconductor (DMS) systems. Li-doped ZnO is one of the most intensively studied d 0 ferromagnetic semiconductor because it can produce ferromagnetic properties at room temperature and at the same time regulate the conductivity type of the semiconductor. However, the room temperature ferromagnetic properties of Li-doped ZnO materials are still affected by the growth and synthesis methods. Therefore, the aim of this research is to study the growth of Li-doped ZnO thin films by aerosol-assisted MOCVD (AA-MOCVD) method as d0 ferromagnetic semiconductor materials and investigate the room temperature ferromagnetic characteristics and magnetotransport properties. ZnO thin films were grown on Si(100) substrates whitin a temperature range of 200 °C to 400 °C. ZnO thin films were characterized to identify the effect of substrate temperature parameters on the physical properties of ZnO thin films to obtain the optimum growth temperature. Li-doped ZnO thin films were grown with Li doping concentrations from 0 to 20 mol%. Li-doped ZnO thin films were characterized to analyze the effect of Li doping concentration on the physical properties of thin films, especially ferromagnetic properties at room temperature. Magnetotransport measurements were performed on ZnO:Li/Si and ZnO:Li/ZnO junctions through I-V measurements under the influence of external magnetic field and junction magnetoresistance (JMR). The ZnO thin films with various substrate temperatures have a hexagonal wurtzite (P63mc) polycrystalline structure. Substrate temperature can increase crystallinity and change the crystal orientation preference of thin films. The concentration of C impurity in ZnO thin films decreases with increasing substrate temperature and disappears at 400 °C. All ZnO thin films have p-type conductivity due to the formation of oxygen vacuoles and Zn interstitials. Increasing the substrate temperature decreases the resistivity and increases the Hall mobility as an effect of increasing crystallinity. The optimum substrate temperature selected for growing Li- doped ZnO thin films by AA-MOCVD method is 400 °C. ZnO thin films with Li doping concentrations from 0 to 20 mol% grown with a crystal orientation preference in the (002) plane. The Li doping concentration distorts the ZnO crystal structure caused by the incorporation of Li ions in the form of substitutional and interstitial Li. The incorporation of Li ions into the ZnO crystal matrix reaches saturation when the doping concentration is 15 mol%. Li ion incorporation is dominated by substitutional Li compared to interstitial Li. The presence of substitutional and interstitial Li incorporation together with interstitial Zn can be an indication of the formation of Zn vacancy. The conductivity type of Li- doped ZnO changes to p-type starting from 10 mol% Li doping concentration. The Li-doped ZnO thin films show soft ferromagnetic properties with the presence of a hysteresis loop curve on the M-H curve. The saturation magnetization value of Li- doped ZnO thin films increases up to 15 mol% doping concentration and decreases slightly at 20 mol% concentration. The highest saturation magnetization value is achieved in ZnO thin films with 15 mol% Li doping which is 0.068 emu/g. The magnetic transport measurement results on ZnO:Li/Si heterojunction and ZnO:Li/ZnO homojunction devices showed a change in the I-V curve when given a magnetic field of 0.38 T which indicates a magnetoresistance effect. The JMR value of the ZnO:Li/ZnO homojunction device is greater than that of the ZnO:Li/Si heterojunction device due to the influence of the conductivity difference at the boundary between layers. The change in JMR value of ZnO:Li/ZnO homojunction device with respect to Li doping concentration shows the influence of magnetization on spin accumulation at the boundary between layers. From the results of this study it can be shown that Li-doped ZnO thin films have ferromagnetic properties at room temperature. The measured JMR value at the junction of ferromagnetic and semiconductor materials indicates that Li-doped ZnO thin films have the potential to be developed as materials for spintronic applications.