Effect Of Intrinsic Point Defects On Room Temperature Ferromagnetic Properties And P-Type Conductivity Of ZnO Thin Films

Zinc oxide?ZnO?,as a?-?direct wide band gap?3.37eV?semiconductor material,has a band gap similar to that of gallium nitride?GaN?at room temperature.The exciton binding energy is up to 60 meV,which is twice as much as that of GaN?about 25 meV?.It's expected to achieve room temperature exciton light emitting devices and low threshold laser devices.They are the most competitive blue or ultraviolet optoelectronic devices materials after GaN,and are widely used in the field of short wavelength optoelectronic devices and diluted magnetic semiconductors.For the research of ZnO materials,there are many controversial directions including:First of all,the applications of ZnO in diluted magnetic semiconductors,especially the origin of room temperature ferromagnetism of undoped ZnO thin films are controversial.Although most researchers believe that room temperature ferromagnetism is closely related to intrinsic point defects(V_Zn,V_O,Zn_i,O_i)in ZnO,but their conclusions contradict each other.Secondly,the p-type transformation and stability mechanism of p-type doped ZnO films are not clear,but people gradually return to the essence,and it is considered that the point defects in ZnO play an important role in the transition.Based on the above two questions,this paper has done two different experiments to explore.on the one hand,pure ZnO thin films were prepared on the a-,c-m-and r-plane sapphire substrates by RF magnetron sputtering.on the other hand,a large number of In-N co-doped p-type ZnO thin films were prepared by means of RF magnetron sputtering,ion implantation and annealed,and some samples were accelerated by low temperature in the later stage.Combined with modern detection technology,a series of studies have been carried out on the regulation of defects in the ZnO film,the p-type transformation mechanism and its stability,and obtained the following main conclusions:1.Different orientations of sapphire substrates have a great influence on the defect types and densities of pure ZnO films.The defect density of ZnO thin films on a-plane sapphire substrate is the largest.ZnO thin films on c-plane sapphire substrate are easier to form V_O defects,and V_O concentration is the highest.2.The d⁰ ferromagnetism observed in the undoped ZnO film is independent of the intrinsic defects of the ZnO film,and its more likely derived from the ZnO/Al2O3 interface effect.3.The success rate of p-type ZnO:In-N films can be increased from about 20%to about 80%by changing the traditional process of one-time annealing to realize p-type thin films by adding annealing several times,including time and atmosphere change.The p-type sample obtained by high temperature annealing did not reach the optimum performance.4.The post low temperature treatment can still eliminate part of Zni and further improve the p-type conductivity of the film.With the increase of heat treatment times,the Zni defects in p-type ZnO films increase instead?continuously compensating holes?,and eventually changes to the n-type conductivity.That is,the Zni defect may be an important factor leading to the p-type transition of ZnO:In-N films,and its also significant for the p-type stability of the films.