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Preparation of ZnO-based Magnetic Semiconductor and Its Magnetic Properties

Author: AiZhiWei
Tutor: LiuChang
School: Wuhan University
Course: Microelectronics and Solid State Electronics
Keywords: Diluted Magnetic Semiconductors (DMS) Room-TemperatureFerromagnetism (RTFM) ZnO Nanoflowers Surface Modification Cu2O/ZnOHeterostructures
CLC: TN304
Type: PhD thesis
Year: 2013
Downloads: 98
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Abstract

This thesis will generally introduce the basic theories of Diluted Magnetic Semiconductors (DMS) and the structure of ZnO, as well as the properties and applications of the ZnO-based DMS. After doping magnetic cation Cu into the film of ZnO, room-temperature ferromagnetism appears. Since Cu and its oxides are not magnetic, this ferromagnetism does not come from any magnetic impurities but the intrinsic magnetic property of ZnO:Cu. The electron configuration of Cu is3d104S1, so Cu+doesn’t have any unpaired d electron. But Cu2+has an unpaired d electron, this d electron causes magnetic property in ZnO:Cu. Cu-doped ZnO thin films were prepared by Pulsed Laser Deposition (PLD) with Si substrates, and results shows that our samples reveal the ferromagnetism. However, when we introduce some electrons into these samples by doping some A1atoms, the ferromagnetism will be weakened and disappeared. In addition, the influence of thermal treatment on the ferromagnetism has been studied. After annealed in the atmosphere of Ar and at the temperature of700℃,2%and5%Cu-doped sample show paramagnetic; while the sample doping with8%Cu stays the same ferromagnetism. All these experimental results show that, p-type ZnO is not a necessary condition to determine DMS’s ferromagnetism but the concentration of n-type doping carriers will affect the film’s magnetism. When the electronic carriers have low concentration, ZnO:Cu film displays room-temperature ferromagnetism. Models are introduced to explain why the saturation moment of the sample decreases when extra electrons are introduced.In, the preparation of ZnO film, when the oxygen vacancy is little, i.e. low electron concentration, Cu will likely lose electron and become Cu2+(3d9) in ZnO lattice. Each unpaired electron in the Cu-ion can supply a magnetic moment of1.73μB. The more doping of Cu, the bigger the saturation moment becomes. Contrarily, when electron concentration is high, Cu-ion is more likely to become Cu+(3d10), thus saturation moment decreases. And when the electron concentration becomes even higher, room-temperature ferromagnetism may disappeared. When ZnO thin films are prepared under different condition, its property may vary greatly, which can explain why there have been reports that ZnO film with the same doping magnetic cation doesn’t have room-temperature ferromagnetism. This experiment shows whether it’s n-type semiconductor or p-type semiconductor, there will be a room-temperature ferromagnetism with doping some magnetic cations. In other words, p-type semiconductor is not a necessary condition. N-type semiconductor will also produce room-temperature ferromagnetism as long as the concentration of electronic carriers is not too high, which is proved by the work done here. Moreover, research has been done on the relation between Cu’s valence state and its magnetic property.By using means of Reaction Vapor Deposition (RVD), ZnO nanoflowers are successfully prepared on Si substrate. In order to enhance the optical properties of the ZnO nanostructures, surface modified process has been done by using Atomic Layer Deposition (ALD). A very thin ZnO film is coated on the ZnO nanostructure. It turns out that the coated thin film can effectively improve its optical performance without changing the surface morphologies of nanostructure, which will lead to the possible applications of nanostructures.Cu2O, as an intrinsic p-type direct-gap semiconductor, has drawn great attention recently. By using ALD and magnetron sputtering methods, p-type Cu2O and n-type ZnO heterostructures are successfully prepared and are proved to have rectification characteristics. All the work contributes to further obtaining transition-metal oxides semiconductor and lays the foundation of the appliance of this semiconductor heterostructure.

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