Co-doped ZnO Based Diluted Magnetic Semiconductors

Perhaps the most surprising and potentially-significant claim to have been made inmagnetism thus far in the 21st century is that nonmagnetic semiconductors and insulatorssuch as ZnO or TiO₂become ferromagnetic at room temperature and above when they aredoped with just a few percent of a transition-metal cation such as V, Cr, Mn, Fe, Co or Ni.ZnO is an interesting direct wide bandgap semiconductor that is being explored for numerousapplication. Transition metal doped ZnO is a promising candidate material for the field ofspin-electronics. Spin-electronics is based on concepts that utilize the quantum mechanicalspin properties of carries in addition to the carrier change in realizing electronic functionality.Dilute magnetic semiconductors （DMS）-semiconductors doped with a few percent ofmagnetic atoms-are being actively investigated in the development of spintronic devices.ZnO-based diluted magnetic semiconductors can be prepared by various methods, such aspulsed laser deposition （PLD）, sol-gel method, atomic layer epitaxy （ALE）, metal organicchemical vapor deposition （MOCVD）, molecular beam epitaxy （MBE）, sputtering, andultrasonic spray pyrolysis, etc. Among them, laser molecular beam epitaxy （LMBE） is a newtechnology with high precision developed based on the traditional MBE and PLD techniqueto grow thin films. In this technique, the high energy laser beam incident to the target toproduce plasma and the plasma deposite on substrates to form thin films in a ultrahighvacuum environment. In our experiment, LMBE technique was utilized to grow goodcrystalline quality Co-doped ZnO DMS thin film with room-temperture ferromagnetism.In this study, LMBE technique was used to grow high quality ZnCoO thin film onsapphire substrate and silicon substrate. The influlence of oxygen partial pressure, substratetemperature and the valence state of Co on structure and magnetic properties of the films werealso studied. The main content is as follow:1.A brief introduction of research progress of ZnO-based DMS, and preparations methodsand research significance of ZnO-based DMS.2.An introduction of LMBE and high quality ZnCoO thin films with room-temperatureferromagnetism were grown on sapphire substrates using LMBE. 3. The influlence of oxygen partial pressure on structure and properties of the films werestudied. ZnCoO thin films grown under different oxygen partical pressure were analysed byX-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, UV - visible （UV-Vis）transmission spectroscopy, Raman spectra and photoluminescence spectra （PL） etc.4. The influlence of Co element valence state in ZnCoO thin films on magnetic propertiesof the films were studied. ZnCoO thin films were grown on sapphire substrate under differentgrowth conditions, XPS and depth profiling XPS as a highly sensitive test method to study Coelement valence state in ZnCoO thin films. The characteristics of typical samples existingsignificant differences were shown.5. Room-temperature ferromagnetic ZnCoO thin films with good crystalline quality weregrown on Si（111） substrates. The influlence of substrate temperature on structure andmagnetic properties of the films were also studied.