The Study Of Structure, Magnetism And Optical Properties In ZnMgO Thin Films

Since the potential tremendous applications in the futurespintronics devices, the study of diluted magnetic semiconductormaterials has aroused a lots of attention. In recent years, theresearch on wide direct band gap oxidate semiconductor materialswith room temperature ferromagnetism caused by doping with3dtransition metal has made great progress, nevertheless, there hasbeen a large controversy on the origin of magnetism. Recently, the d0ferromagnetism in non-transition metal doped and un-doped oxidatethin films has greatly aroused researchers’ study interest, in thiskind of material, it is unnecessary to consider the inner magnetismmay be due to the contribution of secondnary magnetic impurities,therefore, we can study better the way defect influence themagnetism in materials. In this work, the pulsed laser depositionmethod has been used to prepare several series of ZnMgO thin filmsdeposited under different oxygen pressure, and we analyzed the influence of varying oxygen pressure and Mg content in targets onthe structure, magnetism and band gap in the thin films. what’s more,we studied the relationship of oxygen vacancy, magnetism and bandgap in the films which have exactly the same preparation methods.Moreover, we discussed the influence of different deposited oxygenpressure on structure, magnetism and band gap in the ZnMgCoO thinfilms which deposited under varying oxygen pressure. The maincontents are as follows:(1) Zn0.9Mg0.1O epilayers were deposited on double-face polishedc-sapphire substrates at temperature of600℃by pulsed laserdeposition technique within a series of deposition oxygen pressure insequence. We find that the c-axis orientation lattice constant of thefilm is decreasing along with the increasing oxygen pressure,accordingly, the ZnO(002) peak is found to shift to lager2θ value; Anddue to the Mg content in the films is inversely proportional with thedeposition oxygen pressure, the band gap of the film is decreasingalong with the increasing oxygen pressure; However, may be due tothe effective concentration of oxygen vacancy in the film isincreasing along with the increasing deposition oxygen pressure atfirst, then to a certain degree,the crystalline of the film becomebetter and the number of oxygen vacancy in the film became less, sothe RTFM of the Zn0.9Mg0.1O epilayers presents an trend of decline after the first rising. In order to verify the conclusions mentionedabove, we prepared some Zn0.85Mg0.15O epilayers which have identicalpreparation conditions with the Zn0.9Mg0.1O epilayers, and obtainedthe same change rule. At the same time, the Zn0.90Mg0.10O alloyceramic target was used to made films at a fixed oxygen pressure(1mTorr), and all the films have exactly same deposition conditions.The study found that the oxygen vacancy not only can control the RTFMin films, but also can regulate the band gap of the films. With theincreasing concentration of oxygen vacancy, the Ms became greaterand the band gap became narrow.(2)We use pure ZnO ceramic target and Zn0.95Mg0.05O, Zn0.90Mg0.10O,Zn0.85Mg0.15O alloy ceramic target made by solid state reaction methodand double-face polished c-sapphire substrates to prepare a series ofZn1-XMgXO films that the deposition oxygen pressure are vacuum and20mTorr respectively. Because the radius of Mg2+is smaller than Zn2+,the x-ray diffraction results showed that the2θ value of ZnO(002) peakis increasing along with the increasing of Mg content in the target;And due to the band gap of MgO is wider than ZnO, so the film whichcontains more Mg will have wider band gap; Nevertheless,for the Mgcontent increasing in the film, the RTFM presents an trend of declineafter the first rising, and the maximum value centered at x=0.10, thepossible reason of this phenomenon is defects and holes which contribute to RTFM are brought by Mg doping in ZnO crystal in thebeginning, but if the defects and holes becomes too much in the films,the effective concentration of oxygen vacancy in the film will be less,which will cause the effective defect concentration falling.(3) The pulsed laser deposition technique and solid state reactionmethod are used to deposit Zn0.85Mg0.10Co0.05O thin films on transparentAl2O3(0001) substrate at600℃under varying deposition oxygenpressure. Along with the increasing of oxygen pressure, the ZnO(002)peak of films shift to higher2θ value, the band gap gradually narrow,and the RTFM of the Zn0.85Mg0.10Co0.05O thin films presents an trend ofdecline after the first rising, which has the same regularity withZn0.90Mg0.10O and Zn0.85Mg0.15O thin films.