Electric Field Modulated Electrical Properties Of Al:ZnO/PMN-PT Heterostructures

In the oxide semiconductor films/ferroelectric substrate heterostructures,the electrical properties of the semiconductor films can be effectively modulated by the reversal of ferroelectric polarization under external electric fields.In this work,a series of Al:ZnO（AZO）semiconductor films were deposited on the[001]-oriented Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃（PMN-PT）single substrates by RF magnetron sputtering.The effects of the ferroelectric polarization and illumination on the semiconducting properties of the AZO films were investigated.In the AZO/PMN-PT heterostructures with the AZO films thicknesses of 20,60and 125 nm,the AZO films exhibit the high/low resistance switching due to the polarization reverse of the PMN-PT under pulse electric fields.Moreover,it was found that the modulation becomes larger as the film thickness decreases.In the AZO/PMN-PT heterostructures with the 125-nm thick AZO films,the relative change of the resistance is～3.4%,while in the AZO/PMN-PT heterostructures with the20-nm thick AZO,the change of resistance can reach～136%.These results prove that the dominated ferroelectric field effect is an interface effect.Under the electric fields,the ferroelectric polarization causes the accumulation/depletion of electrons at the interface,which results in the change of the AZO films carrier density and resistance.In addition,the relaxation behavior of the resistance was observed under the pulse electric fields,which is caused by the competition between the vacancy trapping electrons and the migration of oxygen vacancies.By controlling the oxygen flow rates（R_O）during the growth of the AZO films,we fabricated the AZO/PMN-PT heterostructures with different oxygen vacancy densities.In the n-type semiconductor AZO films,oxygen vacancies act as electron donors.As the R_O increases,the content of oxygen vacancies of the AZO films decreases.Therefore,the carrier density decreases and the resistance increases.Under the ferroelectric polarization,the relative change of the resistance of the AZO films with lower carrier density is more obvious.In addition,the surface potential of the AZO films under the light off and on were measured by Kelvin probe force microscope,and the surface potential increases under light on.The observed gradual increase of the surface potential is suggested to come from the relaxation effect of the photoconductivity.Under the combined effect of ferroelectric polarization and light,the multi-level semiconductor properties of the AZO films can be achieved.