Studies On The Electronic Structures And Magnetism Driven By Defects In Sc Doped ZnO Thin Film

Recently, it has been one of the most important issues torealize diluted magnetic semiconductor with its criticaltemperature equal or above room temperature. Besides, thin filmswithout partially filled d or f shells of transition metal orrare earth element but exhibit Tc above room temperature havearoused public interest. We theoretically studied the possibleferromagnetism origin in ZnO thin film with 5% Sc doping by usingplane-wave pseudo-potential method based on the state-of-artDFT. Generally, In DMS materials the delocalized conduction bandelectrons and valence band holes interact with the localizedmagnetic moments associated with the d or f electrons in magneticatoms. However, those materials such as ZnO thin film with 5%Scdoping, HfO2 thin film, CaB6,SrB6 and radiated graphite allcontain no partially filled d or f shells of transition metalor rare earth element, but exhibit Tc above room temperature.Considering that all of them are film materials ,and ,it is wellknown that the film materials have larger ratio of area andbulk ,therefore the intrinsic defects during the growth of thinfilm would have great influence on there physical properties.As for CaB6 and SrB6, it has been proved experimentally that themagnetic moment per formulas in thin film is two or four timelarger in orders of magnitude than that in the single crystalor polycrystalline materials. And the theoretical calculationsrelated to it proved that the B6 vacancy in CaB6 carries a magneticmoment of 2.4μB. As for HfO2, it has been reported that the thinfilm exhibits ferromagnetism with Tc above 500K, but no in thebulk materials. And calculation on HfO2 proved that the Hfvacancy in HfO2 exhibits a magnetic moment of 3.5μB, and themagnetic moments are ferromagnetic coupled. As for graphite, ithas been proved experimentally that the nonmagnetic graphitewould exhibit ferromagnetism after it is radiated with highenergy particles. And calculation proved that vacancy or thecomplex of vacancy and hydrogen carries magnetic moment. As forZnO, it is well known that ZnO is non-ferromagnetic. Andtheoretical calculation showed that ZnO with one Zn atomsubstituted with Sc exhibited no ferromagnetism. Defects insimple oxides that trap two electrons or two holes are known tohave triplet ground state or low-lying triplet excited state.The role of the dopant is to stabilize the triplet ground state.It will produce Zn vacancy in (Zn0.95Sc0.05)O when Zn+2is substitutedwith Sc+3,therefore Zn vacancy will play an important role in ZnOthin film with Sc doping .we theoretically studied the effectof Sc on the VZn so as to search for the possible ferromagneticorigin.Firstly, I studied the influence of the intrinsic defectssuch as VO= and VZn on the magnetism of ZnO thin film. And I got1.8μB/VZn in Zn15O16, but not in Zn16O15. Secondly, we studied theeffect of Sc on the magnetism. We performed spin-polarizedelectronic calculation on the supercell Zn14Sc1O16, whichcontains Sc and VZn. We got 1.0μB/VZn. In order to simulateactual doping :two Sc atoms will introduce one VZn, We got netmagnetic moment of 0.4μB/VZn, which agrees well with theexperimental result 0.2-0.3μB/VZn. Thirdly, we studied thechange of magnetic moment with the distance of Sc and VZn. Wegot that: it results no change on the magnetism moment, butthe redistribute of magnetic moment on the neighboring atoms.We also calculated the effect of Sc on the formation energyof VZn. We got that: With the introduction of Sc, the formationenergy of VZn reduced apparently, which means Sc favors theformation of VZn .We also calculated and compared the totalenergy of Zn14Sc1O16 with the magnetism moment coupledferromagnetically and antiferromagnetically. We got that theferromagnetic configuration has smaller energy. Then we drawa conclusion that: VZn is the origin of ZnO thin film with 5%Sc doping.