Fe-doped ZnO Diluted Magnetic Semiconductor Prepared By Sol-Gel Method

Diluted magnetic semiconductor (DMS) is a kind of novel semiconductors, which is formed by using magnetic transition metal ions or rare earth metal ions to randomly replace the non-magnetic cations in semiconductors. It can utilize both of charge and spin of an electron simultaneously in hopes of being applied into the novel electronic materials and devices, so it is attracting people's more and more attention. In this thesis, we use a sol-gel method to prepare Fe-doped ZnO DMS compound powders. On the base of large amounts of processing explorations, we made a primary discussion and analysis for the observed room-temperature (RT) ferromagnetic state in the samples as well as its origin in combination with the structure analysis, the bonded state, the optical characteristic and the magnetic behavior of the samples.Firstly, a fit of preparation steps to produce this kind of Fe-doped ZnO compound powders with single wurtzite phase and RT ferromagnetism are explored. The experiment reveals that L-Ascorbic acid plays a vital role in the sample preparation. It can effectively protect Fe²⁺ ions from oxidization in the air and then smoothly enter into the ZnO lattice to do the random replacement and remain the single ZnO wurtzite structure. The dopant Fe ions can uniformly disperse into the ZnO lattice in accordance with ideal random substitution and exist in bivalence as their major valence state. At the same time, the lattice volume increases with the augment of Fe doping concentration. The characteristic of band-edge excition luminescence for Fe-doped ZnO powders appears red shift in contrast with that for pure ZnO powders and meanwhile the peak intensities decrease with the increment of dopant concentration. All Fe-doped samples perform obvious ferromagnetic properties and as the concentration of dopant Fe increases, the saturation magnetization (Ms) is also correspondingly enhanced. It might be induced by the advantage ferromagnetism won through its competition with antiferromagnetism.Secondly, the structural, optical and magnetic characteristics of n-type dopant In or p-type dopant Na co-doping with Fe into the ZnO powder samples are all in further research. The results illustrate that In or Na co-doping with Fe into ZnO DMS powders all keep their original single wurtzite and hexagonal structure. And in the optics measurement, the original band-edge luminescence peak induced by transition of band-edge excition vanished. The magnetismmeasurement of In doped samples reveals that the original ferromagnetism turned into antiferromagnetism, which gradually develops into paramagnetic state. However, the introduction of Na dopant brings a great enhancement of RT ferromagnetism existed in the original samples. These in all can get reasonable explanations in the ferromagnetism-antiferromagnetism competition mechanics.