A First-principles Calculation Study On The D⁰Ferromagnetism Of ZnO And In₂O₃Semiconductors Modulated By Various Defects And Strains

Oxygen diluted magnetic semiconductor （ODMS） is a kind of important materialfor application in spintronic devices. For a long time, many researches have focusedon the conventional semiconductors or wide gap oxides semiconductors with dopingtransition metal or magnetic cation （including3d or4f orbit） in optical catalytic andoptoelectronic properties. In the recent ten years, many research groups found thatsome non-magnetic semiconductor materials especially non-magnetic oxidesemiconductor materials can induce magnetic moment on the premise of not mixedwith magnetic impurities. Coey, a academician of the Royal Academy of sciences,gives a name to this kind of ferromagnetism phenomenon with "d⁰-ferromagnetism".Electronic structure and magnetic properties of these materials have attractedwidespread attentions. It is found that it is necessary to explore the possibility ofchanging the non-magnetic semiconductor into the ferromagnetic semiconductor bythe intrinsic defects or non-magnetic element doping.In this paper, we choose transparent conductive oxide semiconductor ZnO/In₂O₃as a prototype material to study the hole-induced d⁰-ferromagnetism byfirst-principles methods. It includes analyzing the influence of the intrinsic defect ornon-magnetic atoms doping on electronic structure and d⁰magnetism, exploring thespin switching characteristics under the condition of stress and strain. Someinnovative results have been obtained as following:（1） The electronic structure and magnetic properties of ZnO/In₂O₃associatedwith intrinsic defects have been theoretically studied. We may conclude that the holestates induced by the p-type defects reside on the oxygen ion sites, displaying ananisotropic, delocalized spatial distribution. Meanwhile, the electron carriers donatedby n-type defects displaying an isotropic, s-like orbital character. The holes inducedby p-type defects are spin-polarized, and induced magnetic moment. While theelectron carrier show no spin polarization without any addition magnetic moment. Theresults confirm the fact that the intrinsic p-type defect is the origin of the d⁰magntiesm in undoped ZnO/In₂O₃. Therefore, the intrinsic p-type defect is a keyfeature to mediate ferromagnetic coupling, and the cation vacancy or interstitialoxygen atoms is the mainly origin of the d⁰magntiesm.（2） Using the first principle calculations, we revealed that the hole-inducedd⁰-ferromagnetism in ZnO can been enhanced through compensated donor-acceptor. In general, the chemical compound with single defect have higher defect formationenergy, especially the defect formation energy of the p-type oxide semiconductorcontaining single defect is relatively high. We found that the hole-inducedd⁰-ferromagnetism is limited due to the spontaneous formation of intrinsic cationvacancies or extrinsic acceptor. To solve this problem, we proposed an effectivepassivated codoping approach to reduce the formation energies of the acceptors bydoping the host with passive donor-acceptor complexes. It is demonstrated that theformation energies and polarization energies of VZnor NOin ZnO can be reducedsignificantly by doping Ga_Zn+NOcomplexes, while leaving the magnetic moment inthese supercells almost unchanged, which finally improve hole-inducedd⁰-ferromagnetism in the host.（3） Based on the first-principles band-structure calculations, we found that thesurface oxygen dangling bonds and indium vacancy may be responsible for theunexpected ferromagnetism in undoped In₂O₃quantum dots （QDs）. The surfaceoxygen dangling bonds can produce a magnetic moment of6μB and an indiumvacancy （VIn） produce a magnetic moment of3μB, which primarily distributed on thesurface oxygen atoms and the six O nearest neighbors of the vacancy center,respectively. According to the calculated spin density of states, we really observed themagnetic moment derived from the surface anion dangling bonds at the QDs while thesurface cation dangling bonds can not generate any magnetic moments. However,when all the surface dangling bonds are pssivated by peeudo-hydrogen atoms, thecation vacancy become to play a critical role in magnetism, which mainly locates atthe internal O atoms closed to the In vacancy center. It is also found that VOcan notinduce any magnetic moment.（4） We have investigated the effect of isotropic strain on the electronic andmagnetic properties of In₂O₃doped with C impurities. Based on the first-principlesspin density of states calculations, we found that the host shown some magneticmoment due to the C atom substitute for O atom. The spin moment of C substitutionaldefect remain unchanged under the compressive stress, while the spin momentexhibits a sharp transition to a higher value of⁴μB with the applied tensile strain to²%and the value remains almost constant as the strain is further increased.According to our calculations, this phenomenon of the spin moment is weaklydependent on the orientation of the applied strain. A detailed analysis indicates thatthis strain tunable spin moment results from changes in the distance of the two Catoms. The magnetic moment of In₂O₃: C system mainly comes from the p-p coupling of C and O atoms. However, the magnetic moment mainly comes from s-p coupling（the s orbit of C atom） and p-p coupling when the In₂O₃: C system subjected to tensilestrain.