Molecular Beam Epitaxial Growth And Electronic Transport Properties Of MnTe And Ag₂Te Thin Films

In transition metal tellurides,there are many novel physical and chemical properties and broad application prospects in many fields such as optoelectronics,thermoelectric,and magnetic storage.In this study,high-quality nickel arsenide（Ni As）-type MnTe thin film and monoclinic Ag₂Te thin film samples were prepared on single crystal substrates of perovskite oxides using MBE technology,and their structures,morphologies,and electronic properties were extensively studied,achieving the following results:（1）The growth conditions of MnTe thin film samples on Sr Ti O₃（111）single crystal substrates were optimized by varying the temperature of substrate and Mn source,it was found that MnTe thin films deposited under the conditions of substrate temperature of 275^oC,Mn source temperature of 802.5^oC,and Te source temperature of 300^oC achieved high-quality epitaxial growth.By measuring the magnetic and electronic transport properties of a 70 nm-thick film sample,it was found that MnTe thin films exhibited antiferromagnetic behavior and out-of-plane anisotropic magnetoresistance.When an applied magnetic field was perpendicular to the film plane,the film showed positive magnetoresistance effect;yet it showed negative magnetoresistance effect when the magnetic field was parallel to the film plane.Temperature-dependent resistance measurements of the MnTe thin film sample showed a transition from semiconductor-metal-semiconductor conductivity behavior as the temperature decreased from 300 K to 2 K.（2）A group of Ag₂Te thin films with preferred orientation and thicknesses ranging from 20～60 nm were successfully prepared on LaAlO₃（001）single crystal substrates.By studying the thickness-dependent electronic transport properties of the Ag₂Te films,it was found that the films exhibited negative magnetoresistance effect within the thickness range of 20～26.8 nm,and positive magnetoresistance effect within the thickness range of 28.5～60 nm.The positive magnetoresistance effect gradually increased with increasing film thickness,reaching 77%at 14 T in the 60nm-thick Ag₂Te film.The magnetoresistance curves of the films with thicknesses increasing from 30 to 60 nm changed from the typical parabolic shape to a linear form at temperatures below 200 K.Hall effect measurements showed that the Ag₂Te films with different thicknesses were all p-type conductive,and the mobility of the films at 2 K increased by about 22 times as the film thickness increased from 20 to 60 nm.