Preparation And Properties Of Bi₂Se₃ Thermoelectric Materials And Its Application In Thin Film Field Effect Transistors

As a new material form,topological insulators have attracted much attention recently.As a strong topological insulating material,Bi₂Se₃ has a Dirac point on its surface state.At the same time,it has the characteristics of controllable stoichiometric ratio in preparation,easy to synthesize high-purity chemical phase materials,and can be widely used in thermoelectricity,optoelectronics and new transistors.It has been attached great importance to researchers all over the world.In this paper,the preparation of undoped Bi₂Se₃ thin films and cu doped Bi₂Se₃ thin films on different substrates by magnetron sputtering technique was carried out.Its thermoelectric characteristics and application in thin film field effect transistor are studied.The main contents of this paper are as follows:?1?Five groups of Cu/Bi₂Se₃ thermoelectric samples with a mass white fraction of 0?1.639?3.670?5.859 and 9.012%were prepared by dual-target magnetron sputtering.The XRD comparison of the prepared samples was carried out.The thermoelectric voltage,conductivity,thermal conductivity,Seebeck coefficient and thermoelectric value ZT of different samples are studied.The results show that the thermoelectric value of doped Cu/Bi₂Se₃ thermoelectric thin films is better than that of undoped films at the same temperature gradient.The mechanism of improving the thermoelectric properties of Bi₂Se₃thermoelectric thin films doped with Cu is analyzed in theoretically in this paper.?2?Annealing treatment for samples in different temperature,the results found that annealing to improve the thermoelectric Bi₂Se₃ optimal value had no obvious effect.?3?The fabrication and IV characteristics of n-type Bi₂Se₃ thin film field-effect transistors have been studied by sputtering technique.Through the analysis of different conditions on the n channel FETs Bi₂Se₃ thin film device of the IV characteristic,with different channel width,sputtering time,different grid voltage,different percentage of Cu doping amount and annealing conditions,the influence of and the results are analyzed.The results show that the current between the source and leakage electrodes increases with the decrease of channel width and sputtering time,and increases with the increase of Cu doping content.The applied gate voltage can adjust the channel conductance well.When the device channel width of 40 um,sputtering time for 5 min,Cu doping quantity was 9.012%,source level between the leakage current is 0.11 A.This is because the doping of Cu can improve the doping of heavy ions in Bi₂Se₃ due to se vacancies and anti-potential defects,and the Fermi level of Bi₂Se₃ can be moved to the energy levels of the system,so that the transport efficiency of surface state electrons can be improved.It is also found that when the sputtering time and the channel width of the device are the same,the absolute value of the current between the source and drain of the device increases with the increase of the annealing temperature of the device,and the iv characteristic of the device after annealing at 300?is better than that of the device after annealing at 200?.We think this is because the high temperature rapid annealing can eliminate the residual stress in the Bi₂Se₃ semiconductor film,make the grain of the film more uniform,reduce the internal stress of the film,and avoid the cracks in the film layer.It is advantageous to the transmission of electrons in the film.