Research On Ni-doped SiC Gas Sensing Device Based On Chaotic Detection Method

Ni-doped SiC devices will improve the efficiency of the target gas adsorption,while chaotic detection can enhance the sensitivity of the test gas.The combination of the two is of great significance for the development of new low-concentration gas sensors.The wide band gap and chemical inertness of silicon carbide make 4H-SiC as a base material with theoretical exploration and practical application significance.The chaotic circuit is sensitive to the initial value,which provides a new idea for designing a sensor that is high sensitivity and low cost.In this paper,the gas adsorption properties of Ni-doped SiC gas-sensitive devices are studied from two aspects:theoretical calculation and chaotic detection circuit design.The specific content includes the following aspects:Based on the first-principles of density functional theory,the magnetic and optical properties of 4H-SiC(001)doped Ni were studied.The effects of spatial position and doping ratio on magnetic and optical properties were analyzed.The results show that for two-dimensional SiC,the suspended bond and interface effect before doping can produce weak magnetism.The position where Ni is replaced by Si is more stable than the structure formed by C.Comparing the substitution of different amounts of C and Si found that the substitution of the C atom is greater than the magnetic moment obtained by substituting the Si atom.The magnetic moment obtained by the odd-numbered substitution is smaller than the even-numbered substitution.The main reason is that the total magnetic moment decreases due to the frustration of spin selection when doping even times.The electronic structure,magnetic and optical properties of monolayer SiC doped with different quantities of Ni atoms in a specific shape are studied.Interestingly,spin polarization appeared to occur in the structures that were doped with one Ni and 3Ni with triangle structure.However,there was no spin polarization present prior to Ni doping,2Ni doping with linear structure and 4Ni doping with rhombus structure.Because of the system did not appear to be polarized on the surface mainly due to the Spin frustration.Localized spin density densities of d electrons mainly occur near the Fermi level.conduction band of the Ni-doped system moved toward the low energy direction,resulting in a decrease in the band gap.Calculations of the optical properties showed that Ni doping is conducive to the enhancement of photoconduction.This result provides the possibility to study the sensitivity and detection diversity of gas adsorption devices.The effect of applied electric field on the adsorption of CO and methyl was studied based on the calculation of the stabilized structure after Ni doping.The results show that adding a forward electric field is beneficial to adsorption when adsorbing gas but the opposite is beneficial to gas desorption.Therefore,the purpose of gas adsorption or desorption can be achieved by adjusting the magnitude and direction of the electric field.Investigating the influence of the applied electric field on the band gap,it is found that the band gap of the system increases with the increase of the electric field strength when the forward electric field is applied,and the band gap decreases with the increase of the intensity when the negative electric field is applied.Therefore,the electric field of different directions and intensities has a function of adjusting the band gap to improve the sensitivity of the device adsorption.Through the FPGA control capacitor charging and discharging slope ratio makes the circuit work in chaotic state.The resistance value of the measured resistance is calculated according to the change of the chaotic orbital distance,and the linear relationship between the impedance and the gas concentration is established,and the measured resistance value is displayed in real time through LCD1602.In this paper,the effects of Ni doping on the electronic structure,magnetic properties,optics and adsorbed gases of SiC are studied by first-principles calculations,which provides theoretical guidance for the development of sensors based on silicon carbide.The constant-current chaotic detection circuit designed by FPGA as the main control chip provides reference for the change of reaction gas concentration by detecting the change of resistance value.