Epitaxial Growth And Properties Of Layered Selenides And Their Solid Solution Systems

Layered selenides?such as Bi₂Se₃,In₂Se₃,Sb₂Se₃,MoSe₂ et al.?are one kind of significant semiconducting material,which have good performance in photoelectric,thermoelectric and electrochemical aspects.Therefore it shows promising researches and applications,by doping and other technology methods we can deeply study the physical properties of layered selenides.Bismuth Selenide is belongs to traditional thermoelectric material,it was be found to be a strong topological insulator which has widest band gap so far we know,and it is the most promise fundamental material as topological insulator,and it can be utilized under the room temperature.Some research demonstrated when insert other specific element into Bismuth Selenide crystal lattice,the material what we get will show some novel qualities compared with Bi₂Se₃.This thesis focuses on the phase control growth of Bi₂Se₃ and the solid solution system of Bi₂Se₃,and also did some property characterization of this thin film materials.The main works are as following.?1?Utilized Molecular Beam Epitaxy?MBE?method to growth high quality Bi₂Se₃and the solid solution system of Bi₂Se₃ on Si?111?and mica substrate.Studied the influence of the result by changing the flux of Se source,we confirmed that the quality of Bi₄Se₃ can be good when the flux ratio of Se:Bi is 1:1,and when the flux ratio value of Se:Bi is over than 6 we will only get Bi₂Se₃,when the flux ratio value of Se:Bi is between1 to 6we will get the pseudobinary continuous solid solution of Bi₄Se₃-Bi₂Se₃.We also growth Bi₄Se₃ thin film on InP?111?B substrate,however the Bi₄Se₃ can not be got on this substrate.Beside we use RHEED,STM,HRXRD,Raman spectrum to characterize the surface morphology and crystal structure.The Bi₄Se₃ what we got has good performance of crystal quality and also has smooth surface without impurity phase.By Raman spectroscopy,it is found that in Bi₄Se₃-Bi₂Se₃ pseudobinary solid solution,there is a nonlinear relationship between the components caused by strain and Raman shift.Then we measured the electrical and thermal properties of Bi₄Se₃,for 300nm sample the bulk carrier concentration is 2.79×10²⁰cm³,the bulk resistivity is 7.25×10^-4?·cm,the mobility is 3.09cm²·V¹·S¹,Hall coefficient is 2.24×10^-2m²·C^-1,and the Seebeck coefficient is 52?V/K.?2?We researched on the solid solution system of Bi₂Se₃.By using MBE system growth high quality(Bi_1-xSb_x)₂Se₃ thin film on mica,controlling the temperature of Bi and Se source and changing the temperature of Sb,we growth a series of 20nm thickness thin films with different x value,and we calibrated components of the alloy,by formula fitting,the incorporation rates of Bi and Sb on the surface of(Bi_1-xSb_x)₂Se₃ is 75.38%and82.75%,respectively.Utilized RHEED,HRXRD and Raman spectrum to characterize the surface morphology and crystal structure of(Bi_1-xSb_x)₂Se₃ thin film.It was determined that the maximum solid solubility of Sb in ultrathin(Bi_1-xSb_x)₂Se₃ film?about 4nm?is 68%under the condition of non-equilibrium growth of MBE,and the solid solubility decreased to 24%as the film thickness increased.Beside we did UV-Vis-NIR test of(Bi_1-xSb_x)₂Se₃thin film,we find out the transmittance of(Bi_1-xSb_x)₂Se₃ thin film will increase with doping more Sb,it might be the result of carrier concentration decrease by doping Sb.It was found that the absorption peak of(Bi_1-xSb_x)₂Se₃ thin film appears around 4.24?m wavelength,which indicate the optical band gap of(Bi_1-xSb_x)₂Se₃ thin film is close to Bi₂Se₃.