Investigation Of Raman Spectra At Different Temperature And Laser Power Based On Bi₂Se₃ Single Crystals

Bismuth selenide?Bi₂Se₃?is an excellent thermoelectric material with high quality coefficient and has always been an important target in the field of thermoelectric research.Recent studies have shown that Bi₂Se₃ is a new type of three-dimensional topological insulator material.Because of its low toxicity,easy synthesis,simple band structure and large energy system?0.3 eV?,it has great application prospects in spintronic devices,superconductors,optical devices and low-energy electronic devices at room temperature.In this paper,Bi₂Se₃ single crystals were prepared by Bridgman method.The group of Bi₂Se₃ single crystal samples were prepared from Bi₂Se₃ powder with high purity?5N?and optimized growth temperature field.Through many experiments,the quartz ampoules were optimized according to the rule of geometrical elimination.Then,the second group of Bi₂Se₃ single crystal samples was prepared by using high purity?5N?powder of Bi₂Se₃ and adding 5%Se powder.Based on the analysis of X-ray diffraction,scanning electron microscopy and Raman spectrometer,both groups of samples are Bi₂Se₃ single crystals growing along the direction of[001],and have distinct layered structure.The test results show that the grown Bi₂Se₃ single crystal has high lattice integrity and good element ratio with process optimization.The Raman spectrum of the Bi₂Se₃ single crystal block grown under Se-rich conditions was tested in the range of from room temperature to 473 K with a laser wavelength of 532 nm.With increase in temperature,the peak position of A¹_1g,E_g² and A²_1g modes was observed to follow systematic red-shift.Moreover,the Full Width at Half Maximum?FWHM?increases with increase in temperature.The red shift of Raman peaks is related to the lattice expansion caused by temperature rise and the enhancement of non-harmonic coupling between phonons.The increase of FWHM of the Raman peak is only related to the anharmonic coupling between phonons.Selecting a single crystal block grown under Se-rich conditions,the Raman spectra of Bi₂Se₃ single crystal were measured with a laser wavelength of 532 nm and 785 nm.With the increase of laser power,Raman characteristic peaks show obvious red shift and FWHM increased in both laser wavelengths.The reason is that the temperature in the test area increases with the increase of laser power,the anharmonic coupling between phonons leads to the increase of the FWHM of Raman characteristic peaks,and the lattice expansion and the anharmonic coupling between phonons jointly lead to the red shift of Raman characteristic peaks.At the same time,due to the temperature difference between the test area and other areas,phonon scattering also contributes to the frequency red shift and the increase of the FWHM of the Raman characteristic peaks.