Electrical Transport Properties And Application In Vacuum Devices Of Carbon-Based Resistive Wall

Silicon carbide has excellent electrical transport properties such as high saturation carrier drift rate and high conductivity.In this thesis,silicon carbide is to study its electrical transport properties.In order to explore whether silicon carbide materials can further enhance the clustering of electron beams in vacuum electronic devices,this thesis attempts to add silicon carbide resistive wall materials to the double-cavity klystron,and conduct simulation for it.The main work and results of this thesis are as follows:（1）First-principles calculation is carried out on silicon carbide.The pseudopotential and exchange-correlation functional are determined.The Quantum Espresso and Wannier90 software packages are used to calculate the lattice constant,band structure,effective electron mass,phonon spectrum,dielectric constant,and other results of silicon carbide.The lattice constant obtained by the mode-conserving pseudopotential and the PBE exchange-correlation functional in QE is 4.3558（?）.During calculation of the energy band,it is found that using different pseudopotential has less effect on the obtained band gap,while using different exchange correlation functionals has a greater effect on the obtained band gap.According to the calculated band structure,the effective mass of the electron at the bottom of the conduction band is 0.685 m₀.（2）Electrical transport studies are conducted on silicon carbide.The electron-phonon interaction matrix of silicon carbide is obtained by solving the Boltzmann transport equation using the Perturbo software package,and the relaxation time,conductivity,mobility,and other electrical characteristics parameters of silicon carbide are obtained based on the interaction matrix.When the temperature is 300K and the carrier density at the bottom of the conduction band is1×10^{1 8}cm^-3,the relaxation frequency of 3C-SiC is 1.585THz.The electrical conductivity and mobility of SiC at different temperatures and different carrier concentrations were calculated.Under the same temperature,as the carrier concentration increases,the conductivity increases continuously,and the mobility may decrease when the carrier concentration is high due to scattering,electron interaction and other reasons.The dispersion of conductivity,the change of real and imaginary parts with frequency,is calculated.（3）The simulation calculation of klystron which has the silicon carbide impedance wall material and operates in the Q-band and W-band is carried out in CST.Conductivity obtained from electrical transport studies are approximately set as the resistive wall in the simulation.When the operating center frequency is 39GHz,the best output power of the traditional dual-cavity klystron is 61.38W,the gain is 17.880dB.While the best output power with silicon carbide impedance wall is 157.63W,the gain is21.976dB,the output power increased 156.8%.The optimal tube length of the klystron with the silicon carbide impedance wall is shorter than that of the traditional klystron.In the case of small signals in the Q-band and W-band,output power,signal gain and electron injection efficiency of the klystron with the silicon carbide impedance wall have all been improved.The above results show that the silicon carbide resistive wall can not only further cluster the electron beams,but also make the electron beams cluster with higher quality.