Electro-Transport Properties And Their Tunability At The Interface Of New Oxide Heterostructures

The two dimensional electron gas（2DEG）at the interface of oxide heterostructure exhibits a large number of novel physical properties,such as ferromagnetism,2D superconductivity,Rashba spin-orbital coupling,the tunability of the electric field and light illumination,etc.These remarkable physical properties have raised extensive interest of fundermental research workers and make it possible for the achievement of new electronic devices.At present,there are two kinds of substrates which can be used to generate 2DEGs,Sr Ti O₃ and KTa O₃.In this thesis,both Sr Ti O₃-based and KTa O₃-based 2DEGs were researched.Firstly,the La Al O₃/Sr Ti O₃ superlattices with multiple quantum wells were prepared with pulsed laser deposition（PLD）method,which host multilayer two dimensional electron gas.In addition,based on the oxygen vacancy mechanism of the two dimensional electron gas formation,we deposited theγ-Al₂O₃film with spinel crystal structure and zirconium oxide on KTa O₃ substrate to create new2DEGs.The conductive interfaces obtained at specific condition in these samples can be modulated by the electric field or light illumination.The electro-transport properties of the conductive interfaces have been researched systematically.The results of experimental study are summaried as follows:1.The La Al O₃ and Sr Ti O₃films were alternatively grown on Sr Ti O₃（001）substrate with single Ti O₂ termination,and La Al O₃/Sr Ti O₃ superlattices with high quality were obtained.All of samples are well metallic,and two band conduction exist in typical samples.For the superlattices,with the thickness of La Al O₃ fixed,as the thickness of the Sr Ti O₃ decreases,the sheet resistance at low temperature decreases and the density of minority carriers become larger.The conductive carriers can be tuned by the backgate voltage which is applied at the bottom of the Sr Ti O₃ substrate.As the backgate voltage changes,the minority carriers change significantly,and majority carriers keep almost unchanged.The minority carriers mainly exist at the interface of the Sr Ti O₃ substrate,and the majority carriers mainly exist at the post-deposited Sr Ti O₃ films.The separation between majority and minority carriers in space provides alternative materials for the design and production of novel field-effect devices.2.Theγ-Al₂O₃ films were grown epitaxially on the KTa O₃ substrate for the first time.For the deposition temperature from 300 to 700℃,theγ-Al₂O₃ films are crystalline form,and metallic two dimensional electron gas is obtained at the heterointerface.As the deposition temperature decreases,the density of carriers become lower.When the deposition temperature is above 500℃,the critical thickness for the occurrence of the conductive interface is 0.8 nm.And the critical thickness increases to 3.2 nm with the deposition temperarture decreasing to 300℃.The electric properties of the two dimensional electron gas can be modulated by laser.Under the light illumination,the maximum change of the carrier density is up to 3×10¹³ cm^-2,exceeding the maximum change of the carrier density in typical two dimensional electron system.The spin-orbital coupling of the KTa O₃-based 5d 2DEG can also change with the different light power.When the carrier density is 4.5×10¹³ cm^-2,the maximum of the spin-orbital coupling appears,which is 7.9×10^-12 e Vm.The appearance for the maximum of the spin-orbital coupling is perhaps originated from the occupation of the new energy band,i.e.,Lifshitz transition.The reason why the Hall resistance curves under the light illumination do not show the variation from linearity to nonlinearity is perhaps that the mobility of the carriers in different subbands is almost the same.3.The Ca Zr O₃ and Y₂O₃ doped Zr O₂ films were deposited on the KTa O₃（001）substrate,respectively.The heterointerface is conductive for all the deposition temperature from 700℃to room temperature for the Ca Zr O₃/KTa O₃ heterostructure.As the deposition temperature decreases,the carrier density also decreases.The magnetoresistance curves show weak antilocalization effect,which is originated the spin-orbital coupling of the two dimensional electron gas.In addition,Y₂O₃ doped Zr O₂films were also deposited on the KTa O₃substrate.The conductive interface was obtained,only when the deposition temperature is low than 200℃.The carrier density becomes larger with the light power increasing.As the carrier density is larger than3.8×10¹³ cm^-2,the Hall resistance curves change from linearity to nonlinearity,i.e.,Lifshitz transition occurs.The electron occupies at new energy band,and two types of carriers with different mobility exist at the conductive interface.This result opens an avenue for the design of new two dimensional electron system.