Preparations And Properties Of ZnO-based Diluted Magnetic Semiconductors

Diluted magnetic semiconductors (DMS) are semiconductors in which transition –metal ions substitute cations of the host Semicnductor materials. Localized d electrons of the magnetic ions couple with the extended electrons in the conduct band .These couplings lead to a number of peculiar and interesting properties, such as, ferromagnetic, magneto-optical and magneto-electrical effects. Dietl et al. suggested GaN and ZnO as candidates having a high Curie temperature (Tc) and a large magnetization, and lately a few experimental results were reported. A wide-gap Π-VI semiconductor, ZnO attracts attention as a material with possible application in optoelectronic devices such as solar cells, ultraviolet emitting diodes, and transparent high-power electronic devices. The discovery of ferromagnetism (FM) at temperatures above 100K in the Ш-V semiconductor Ga_1-xMn_xAs. Theoretical predictions of room-temperature FM in diluted magnetic semiconductors (DMSs)² recently focused attention on magnetic-ion-substituted ZnO with a wurtzite structure similar to GaAs. The Zn_1-xTM_xO samples in this study were prepared using a standard solid-state reaction technique. Mixtures of ZnO and MnO₂, or Co₃O₄, for TM=Mn and Co, respectively, were fired in air several times at elevated temperatures of 900℃, 1100℃, and 1300℃for about 2 to 4 hours. Afer samples were synthesized ,we would define their crystal structure by XRD and their physical properties,including magnetic properties and so on . For Mn-doped ZnO with 5 at.%,6 at.%,8 at.%,10 at.% fired in the air. We have found that XRD patterns already presented the second phase ZnMn2O4 belonged to Tetragonal crystal system in the sample Zn1-xMnxO(x=0.05),but the diffraction intensity of the impurity ZnMn2O4 is weak, which indicated that the solubility limit the Mn ions in ZnO was less than 5%. We studied the magnetic properties of Zn0.9Mn0.1O which have the impurity ZnMn2O4.The sample Zn0.9Mn0.1O revealed the presence of antiferromagnetic interactions by M-T curve measure. At lower temperatures inverse DC susceptibility curve toward a temperature close to Zero. And we have studied M-H curve of the sample Zn0.9Mn0.1O under RT,70K and 10K temperature. The result revealed that the M followed H leads to a change similar to ferromagnetic material at the beginning of adding to magnetic field and below 200Oe. But there is a difference that M didn't go to a saturation state followed the increased H with ferromagnetism material. It is like that the curve exhibits a paramagnetic behavior,M being linearity increasing followed increasing H.And that the curve exhibits that magnetic field minished which is similar to a ferromagnetic M-H change .When T is 10K tempreture,the change of M followed H entirely similar to paramagnetic behavior.We will more discuss the correlative physics mechanism of above phenomena. The single-phase samples Zn1-XCoxO(x=0.02, 0.04, 0.06, 0.08, 0.10, 0.16,x=cobalt content) were prepared using a standard solid-state reaction technique. The crystal structures of co-doped ZnO were characterized by XRD. The diffraction pattern reveals only the presence of the peaks corresponding to hexagonal ZnO and no second phase peaks.We have found that Co doped ZnO samples are all n-type semiconductors Their carrier concentration are about to be e+17/(cm-3) and the mobility is from 32 to 58cm2/(Vs).