| In traditional semiconductor materials,their physical properties are mainly determined by the electrons of s and p orbitals.Perovskite-type oxide materials,as a strong electronic correlation material,their physical properties are mainly determined by the electrons of d orbitals.Because of the interaction between charge,orbit,spin and lattice,their physical properties are also more abundant.Two-dimensional electron gas with high mobility at the interface of the perovskite oxide La Al O3/Sr Ti O3 have been proposed,which has attracted extensive attention of researchers.Meanwhile,at the interface of La Al O3/Sr Ti O3 heterostructure,other novel physical phenomena also emerge in endlessly,such as superconductivity,anomalous quantum Hall effect,Kondo effect,coexistence of superconducting ferromagnetism.The construction of high-quality oxide heterostructures is the premise of exploring novel physical phenomena at the interface.At the same time,the regulation of the electrical transport performance of oxide heterostructures is the basis of promoting its application in electronic devices.Therefore,this paper mainly studies the preparation of oxide thin film heterojunction by pulsed laser deposition and adjusts the electrical transport performance in the heterojunction by different ways.The metal insulator transition was observed.The main research contents and results are summarized as follows:1.The introduction of the buffer layer Sr3Al2O6 provides the regulation of different in-plane strain on the electrical transport performance of La Ni O3 films.La Ni O3 film and La Ni O3/Sr3Al2O6 heterojunction were grown on Sr Ti O3 substrates by pulsed laser deposition.Due to the different in-plane strain produced by Sr Ti O3 substrate and Sr3Al2O6 buffer layer on the top layer of La Ni O3 film,it can have a certain effect on the octahedral structure of Ni O6 in La Ni O3 and change the valence state of Ni in the La Ni O3film.According to the results of variable temperature electrical transport performance,La Ni O3 film and La Ni O3/Sr3Al2O6 heterojunction show different conductive behaviors.La Ni O3 film shows metal conductivity with reduced resistance as temperature decreases,while La Ni O3/Sr3Al2O6 heterojunction shows semiconductive conductivity with increased resistance as temperature decreases.With the thickness of La Ni O3increasing,the La Ni O3/Sr3Al2O6 heterostructure reduces the resistivity and maintains the semiconductor conductive behavior.2.Different growth oxygen partial pressures bring different oxygen vacancy concentrations to the La Al O3/Sr Ti O3 heterojunction and regulate the Kondo effect at the interface.In order to obtain high-quality oxide heterojunction interface,the（001）oriented Sr Ti O3 substrate was treated by hydrofluoric acid etching and high temperature annealing to obtain a stepped surface with the single cut-off layer of Ti O2.The growth process of La Al O3 films were monitored in situ by reflective high-energy electron diffraction equipped with the pulsed laser deposition and the corresponding growth mode and growth rate were obtained.The growth thickness of La Al O3 film is the same under different growth oxygen pressure.X-ray photoelectron spectroscopy shows that different oxygen pressure will lead to different oxygen vacancy concentration in the heterojunction.According to the electrical transport performance test,the minimum resistance appears at the interface of La Al O3/Sr Ti O3 heterojunction.At low temperature,the Kondo effect that the resistance increases with the decrease of temperature was observed.By fitting and analyzing the resistance with the Kondo effect model,it is proved that the oxygen vacancy has a regulating effect on the Kondo effect at the La Al O3/Sr Ti O3 interface.3.The La0.67Sr0.33Mn O3 covering layer is introduced to construct the La0.67Sr0.33Mn O3/La Al O3/Sr Ti O3 heterojunction and the electrical transport performance of the La Al O3/Sr Ti O3 is adjusted by the thickness of the covering layer.The growth conditions of La0.67Sr0.33Mn O3 films were optimized by pulsed laser deposition and high-quality single crystal epitaxial films were obtained.The growth process of La0.67Sr0.33Mn O3 films was monitored by reflective high-energy electron diffraction and the growth mode and growth rate of the film were obtained.The growth and structural process of La0.67Sr0.33Mn O3/La Al O3/Sr Ti O3 heterojunction were monitored and the thickness of the film was accurately controlled.According to the results of variable temperature electrical transport,the conductive behavior of La Al O3/Sr Ti O3 heterojunction has changed.With the introduction of La0.67Sr0.33Mn O3film coating,it shows a transition from metal conductivity to semiconductor conductivity.With the thickness of La0.67Sr0.33Mn O3 coating increasing,the resistivity decreases gradually. |
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