Electrical And Magnetic Studies Of Wide Band Gap And Narrow Band Gap Diluted Magnetic Semiconductorts

Possessing semiconductor properties and magnetism simultaneously,diluted magnetic semiconductor(DMS)is an excellent candidate for spintronic devices.In this thesis,our studies focus on the electrical properties and magnetic properties of wide band-gap ZnO-based DMS and PbPd"2,a kind of DMS which has zero gap.(PbPd"2 is a kind of gapless semiconductor(GS)).Firstly,Zn1-xCrx" films were prepared using ultrasonic spray method.The influence of doping ratio on structures,optical and magnetic properties was studied.The experimental results indicate that,the Cr doping restrains the preferred orientation of C axis for ZnO;the the average grain sizes of the samples increase after Cr doping and the size attains the maximum when x=3%.Moreover,it is found that Vzn,Zni and Vzn defects exist in the Cr doping films,and Vzn is largest when x=3%.The band gap increases with the doping of Cr and it reachs the maximum when x = 3%.Magnetic measured results show that three doping samples Zn1-xCrxO(x=1%,3%and 5%)are ferromagnetic at room temperature,and the magnetization of Zn1-xCrxO(3%)is largest,which is corresponding to the the most Vzn defect.The experimental results also prove the theoretical prediction that the substitutive Cr in the oxidation state of +3 and the neutral Zn vacancy in the Zn":Cr sample is the most favorable defect complex to maintain a high stability of ferromagnetic order.Secondly,we fabricated PbPdO2 films with(211)preferred orientation(sample A)and with(002)preferred orientation(sample B)by pulsed laser depositon technology.The physical performance differences between the two samples were investigated.The results show that both samples are granular structure with the grain size of about 200nm and the preferred orientation do has evident influence on the physical properties of PbPdO2.With the increase of temperature,the work function of sample A decreased and it stayed constant for sample B,indicating that the sample B possesses the small gap.By electrical measurements,it is found that the sample B possesses lower resistivity compared to sample A.Both samples possess a wide insulator-metal transition temperature(TMI)at around 370K.At last,the experimental results are consistent with the calculated those based on the electronic density of states from first-principles calculations.Lastly,we investigated the influence of ion doping(Cu,Co,Fe)on the structures,electrical and magnetic properties of PbPdO2 prepared by PLD.The results show that the samples turn to a shape of strip with the length of 200nm after Cu,Co and Fe doping.By electrical measurements,it is found that the sample with Fe doping has a higher resistivity,and both samples with Cu and Co doping have lower resistivity.All samples possess a wide insulator-metal transition temperature(TMI),and the TMI shifts to low temperature after doping.Magnetic measured results show that all samples are ferromagnetic at room temperature,and the magnetization of PbPd0.9Fe0.1O2 is largest.