Growth And Physical Properties Of Layered Chalcogenide Thin Films,Heterostructures,and Quantum Structures

Bismuth Selenide?Bi₂Se₃?and other related chalcogenides A₂B₃?such as Sb₂Te₃,Bi₂Te₃,In₂Se₃ et al.?are simple and most popular family of materials which have unique crystal structure and novel physical properties,and show great research and application values in condensed matter physics,quantum spintronics,photoelectric,thermoelectrics and energy areas.Bismuth Selenide,which belongs to traditional thermoelectric material,is newly found to be strong topological insulator with widest band gap?0.3 eV?,and is the most promise fundamental material as topological insulator which is able to be working under room temperature.Meanwhile,the quantum structures of Bismuth Selenide show more predictable novel quantum physics properties and outstanding thermoelectric performance.And this attracts great attention for the research of layered chalcogenides and related quantum structures.However,chalcogenides are confront with huge challenges in preparation of the complex bonding structures which are quite different with regular covalent semiconductors.This thesis focuses on investigation of the basic scientific problems of the thin film and quantum structure of layered chalcogenides.The controllable growth of layered chalcogenides thin film on silicon substrate and electric properties of the thin films,the growth process and dynamics of the nanostructure and heterostructure of layered chalcogenides,and also precision doping and fabrication of quantum structures of layered chalcogenides are systematically studied.Main works are as following.Through home-made physical vapor deposition?PVD?system,we systematically study the procedure and growth model of growing Bi₂Se₃,Sb₂Te₃,Bi₂Te₃ thin film using their compounds as sources on silicon substrate.By research on the effects of chalcogenides thin films crystal structures,morphologies and compositions relationship with source temperature,pretreatment of substrate and also substrate temperature,we obtain growth conditions for making highly c-oriented Bi₂Se₃,Sb₂Te₃,Bi₂Te₃ thin film.This could provide guidance to the epitaxy and heterostructure study of the layered chalcogenides with nowadays most popular semiconductor silicon.The Bi₂Se₃ thin film was sputtered via layer by layer by Ar-ion,and characterized by XPS/UPS on site for the core levels of main elements in film and substrate.We firstly conclude the band diagram between Bi₂Se₃ and H-Si by valence state and energy band feature.This will provide important parameter for the carriers control and photoelectric detection of Bi₂Se₃ and H-Si heterostructure.By the way,through energy diagram of Bi 5d,Se 2p and Si 2p in substrate from the Ar-ion sputterred thin film sample,Van der Waals epitaxy of Bi₂Se₃ on H-Si was also verified,because of sharp interface of the elements profile between film and substrate.The schottky barrier height ?B between Bi₂Se₃ and H-Si is 0.31 eV.The nanostructure fabrication process and growth model by PVD method on various substrates was studied.The preparation of heterostructures of layered chalcogenides by the means of PVD was also investigated.During the growth,we noticed that,Sb₂Te₃ can work as a buffer layer for other layered chalcogenides,but Bi₂Se₃ and Bi₂Te₃ are difficult in such position,due to some decomposition and interdiffusion.Those experimental results can help us in understanding the physical properties of each material better and provide important guidance for heterostructure growth.At the same time,even though the growth model of those layered chalcogenides meets with Van der Waals epitaxy,the well matched lattice and good crystallized film as substrate still has effect on the structure and surface of the film on top.We study the growth kinetics of fabricating high quality Bi₂Se₃ film on large lattice mis-matched Si?111?substrate by Molecular Beam Epitaxy?MBE?.In avoiding of reaction between Se and Si,which can result in defects and polycrystalline,the dangling bonds on the Si?111?-7x7 surface need to be saturated by proper passivated layer.We studied growth kinetics of growing Bi₂Se₃ on Hydrogel and Bismuth passivated Si?111?surface,and found that the growth model of Bi₂Se₃ on the H-and Bi-passivated Silicon is Van der Waals epitaxy.Single crystallized samples with big terraces and the terrace height in quintuple layer?QL?level are fabricated,which lay important material science and technology foundation for the requirement of samples with excellent surfaces.We study the growth of highly c-oriented Bi₂Se₃ film with good crystalline and flat surface on mica substrate by MBE.Further research is carried out to study the unbalance doping of Sb in Bi₂Se₃ thin film and controlling of the carriers.Then the limitation of Sb concentration in Bi₂Se₃ was concluded.The structure,morphology,electric and optics properties of the Sb-doped Bi₂Se₃ thin film were systematically studied,and found the relationship of the doping amount on the carrier concentration and mobility.Controllable Bi₂Se₃/In₂Se₃ superlattice was successfully fabricated on mica by MBE.Using of RHEED and XRD characterization and analysis of both in-plane and out-of-plane,we found that the Bi₂Se₃ and In₂Se₃ consist with each other and share totally parallel?00L?and?015?direction.We study the thermal conductivity difference between M QLs-Bi₂Se₃/ N QLs-In₂Se₃ superlattice and pure Bi₂Se₃ film.And first discover that this superlattice can scatter the phonons of interfaces and thus decrease the thermal-conductivity.This paves way for the application of layered chalcogenides in thermoelectric area.