| Bi2Se3 is a three-dimensional topological insulator material that exhibits high electrical conductivity,good optical transparency,and high durability,making it a promising candidate for use in semiconductor devices.Recent research has shown that p-type doping of Bi2Se3 can significantly enhance its electronic transport and optical properties,thereby expanding its application range.Therefore,the study of the crystal structure,photoelectric properties,and p-type doping characteristics of Bi2Se3 is of great practical importance.Firstly,n-type infrared-transparent conductive Bi2Se3 thin films were grown on an Al2O3(001)substrate using molecular beam epitaxy(MBE)and were subsequently doped into N-Bi2Se3/P-CuScO2 heterojunction diodes for further study.Secondly,based on first-principles calculations utilizing Materials Studio 2019 software,the band structure,density of states,differential charge density,and optical properties of Bi2Se3 were simulated and analyzed.The specific research content is as follows:1.Using MBE(molecular beam epitaxy),n-type infrared-transparent conductive Bi2Se3 thin films were grown on an Al2O3(001)substrate,with a Bi2Se3(001)/Al2O3(1 (?) 10)orientation relationship.The conductive mechanism is small polarized hopping,with an activation energy of 34 meV.The thin film exhibits n-type conductivity,with a room-temperature resistivity of 7×10-4 Ω.cm.The thin film shows excellent carrier mobility of 1,015 cm2/Vs at room temperature,and maintains optical transparency in the near-infrared(>70%)and far-infrared(>85%)ranges.To explore the application of Bi2Se3 thin films,N-Bi2Se3/P-CuScO2 heterojunction diode devices were prepared,with a threshold voltage of～3.3 V that is consistent with the bandgap value of CuScO2.The high optical transparency and conductivity of Bi2Se3 thin films make them very promising in light-electricity applications requiring a wide wavelength range from near-infrared to far-infrared.2.The intrinsic structure of Bi2Se3 was studied.First-principles simulations were used to calculate the intrinsic structure of Bi2Se3,and the results showed that Bi2Se3 is a narrow-bandgap direct-bandgap semiconductor when spin-orbit coupling is not considered.When spin-orbit coupling is considered,the band structure of Bi2Se3 undergoes significant changes,transforming from a direct-bandgap structure to an indirect-bandgap structure.The study found that there is a strong covalent interaction between Se and Bi atoms,with a covalent bond between the two types of atoms.At the same time,it was concluded that Bi2Se3 has strong absorption of short-wavelength ultraviolet light.3.To obtain Bi2Se3 materials with superior photoelectric properties,transition metal element Fe,Ca and Mg were selected for p-type doping modification of the Bi2Se3 crystal cell.For Fe doping,the atomic spin properties need to be determined as a whole.The study found that the system is most stable when Fe is doped in a high-spin state.Then,two systems were calculated for Fe doping with a concentration of single atoms and four atoms symmetrically.The results showed that as the Fe doping concentration increases,the bandgap of the doping system gradually decreases.Next,the doping concentration of Ca(without spin)was calculated for the two systems of single atoms and four atoms symmetrically,and the bandgap of the doping system gradually increases,indicating that Ca opens up the energy gap of the system.Finally,the doping concentration of Mg(without spin)was calculated for the two systems of single atoms and four atoms symmetrically,and the results showed that as the Mg element concentration increases,the bandgap of the system also gradually decreases.The doping effects of Ca,Fe,and Mg on Bi2Se3 were also studied.The formation energy of Ca,Fe,and Mg replacing Bi was calculated,and it was found that the formation energy of single atoms(Ca,Fe,and Mg)doping systems is less than zero,while the formation energy of other doping systems is far greater than zero.This result indicates that the single atom(Ca,Fe,and Mg)doping system can achieve stable p-type doping of Bi2Se3.Furthermore,the formation energy of Ca,Fe,and Mg doping was compared,and the results showed that Fe doping has the best effect,followed by Mg doping,while Ca doping has the worst effect.In summary,this paper systematically studied the intrinsic structure and p-type doping modification of topological insulator Bi2Se3,and obtained some effective conclusions,which lay the foundation for further research on Bi2Se3 materials and their p-type doping. |
PDF Full Text Request