Epitaxial Growth And Physical Properties Of Bi₂Se₃ Superlattices And Thin-film Heterostructures

Bi₂Se₃ is a typical representative of topological insulator materials.Its body energy gap is as high as 0.3eV and has strong resistance to thermal disturbances.So it is expected to become a basic material for spin electronic devices that can work at room temperature.However,the physical properties of a single material are fixed.Preliminary studies have shown that two-dimensional materials,such as superlattices and quantum wells,alternately stacked from Bi₂Se₃ based topological insulator materials and other materials,exhibit lower thermal conductivity and more novel quantum physical properties.These novel physical properties are actually determined by the coupling state of the topological quantum state correlation in low-dimensional conditions,and are related to various structural details of the superlattice or quantum well,so it is also convenient to modulate physical properties by changing the structural parameters of the topological insulator superlattice or quantum well.This article will focus on the preparation of Bi₂Se₃-based superlattices and heterostructures and the frontier direction of the physical properties of heterogeneous interface basic transport.The experimental results obtained can be used to further study the growth dynamics of topological insulator superlattices and quantum well structures,and become a useful reference for the nature of electrical transport.The specific work content and related results are briefly described as follows:1.Using molecular beam epitaxy to prepare four kinds of high-crystal quality thin film heterostructures composed of Bi₂Se₃ and lattice-matched In₂Se₃ on InP?111?B substrates that match the lattice of Bi₂Se₃,which are substrate-Bi₂Se₃-In₂Se₃ type,substrate-In₂Se₃-Bi₂Se₃ type,substrate-Bi₂Se₃-In₂Se₃-Bi₂Se₃ type,and substrate-Bi₂Se₃type.?1?In the high-resolution X-ray diffraction?HRXRD?of the substrate-Bi₂Se₃-In₂Se₃ type heterojunction,it was observed that the independent In₂Se₃ peak position corresponds to the peak position of?-In₂Se₃,indicating that the In₂Se₃ layer in the prepared heterostructures is?phase.?2?The measured I-V curve of Bi₂Se₃/InP?111?B heterojunction at room temperature is linear,which proves that the contact between Bi₂Se₃ and InP?111?B substrate is ohmic;The room temperature I-V curve of the sample containing Bi₂Se₃/In₂Se₃ heterojunction shows certain rectification characteristics,reflecting the effective contact barrier formed between Bi₂Se₃ and In₂Se₃.The study of the electrical properties of the heterojunctions lays the foundation for making heterojunction devices.2.The molecular beam epitaxy technique was used to grow(Bi_1-xIn_x)₂Se₃/In₂Se₃superlattice films with gradient composition on fluorophlogopite substrates,and superlattice samples with different thickness ratios were prepared for comparison.?1?From in-situ reflection high-energy electron diffraction?RHEED?observations,the lattice constant of In₂Se₃ layer gradually increased with the growth,and it is speculated that there is a phase transition from?to?during superlattices growth.?2?When the growth temperature is higher,there is a diffusion phenomenon at the interface between the Bi₂Se₃ layer and the In₂Se₃ layer.Some In atoms diffuse into the Bi₂Se₃ layer to form(Bi_1-xIn_x)₂Se₃ structure,and graded(Bi_1-xIn_x)₂Se₃/In₂Se₃ superlattices were prepared.?3?Ex-situ high-resolution X-ray diffraction?HRXRD?and Raman spectroscopy further confirmed that the In₂Se₃ in the superlattices is the?phase under the growth conditions used.The Raman spectroscopy shows lattice vibration characteristics due to phonon confinement in the superlattices.?4?Moire fringes were seen on the scanning tunnel microscope?STM?scan image of the superlattices surface.It is speculated that Bi₂Se₃ and In₂Se₃ will be stacked by rotating 6°when stacked.This conclusion reveals the stable stacking method of the two materials.