The Determination Of Photo-excited Carrier Concentrations In Semi-insulating 4H-SiC By Raman Spectroscopy

4H-SiC has a wide band gap,high thermal conductivity,and fast saturation speed.Owing to its excellent properties,4H-SiC materials can be used in high-temperature environments and have high requirements for power and frequency devices.The controllability of doped impurities to the conductive properties makes 4H-SiC have a wide range of application prospects.Aiming at its intrinsic excitation and extrinsic excitation,this paper uses Raman spectra analysis and numerical simulation calculation to study the change of its carrier concentration.This is a method without damage to the sample,and the measurement is simple and accurate.The main research results obtained are as follows.When the laser energy is less than the band gap of 4H-SiC,extrinsic absorption occurs,and the semi-insulating 4H-SiC does not generate a large carrier concentration.High-purity semi-insulating(HPSI)and vanadium(V)doped 4H-SiC have different internal defects,and V-doped 4H-SiC and HPSI 4H-SiC have different recombination mechanisms.Although there is a photo-excitation carrier concentration,this concentration is not enough to couple with the longitudinal optical phonon(LO)mode of the Raman measurement,so the mode obtained by Raman spectra analysis is the LO mode instead of the longitudinal optical phonon plasma coupling(LOPC)mode.This mode does not increase with increasing laser power,and the carrier concentration cannot be obtained by LOPC fitting.The carrier concentration of V-doped 4H-SiC and HPSI 4H-SiC under 532 nm laser was obtained by calculating the generation and recombination of the defect center.The carrier concentration of 4H-SiC,which is calculated numerically under intrinsic excitation,increases with the increasing power.V-doped semi-insulating 4H-SiC and HPSI 4H-SiC 4H-SiC have a large carrier concentration under a 355 nm laser.The corresponding numerical simulations of the bipolar plasma dynamics in time and space distribution were carried out through equilibrium equations to obtain larger carrier concentrations,and the concentration has a linear relationship with power.The carrier concentration of 4H-SiC in Raman spectra analysis under intrinsic excitation increases with increasing power,and the tendency of increasing under high power decreases.After plotting the carrier concentration obtained under the laser with different power of 355 nm,the carrier concentration increases with the increasing of power,but it is no longer a linear trend like numerical calculation at high power.The effects of the Raman spectra analysis environment and the thermal effects of the laser on the carrier concentration and longitudinal optical phonon coupling may cause this phenomenon.By two numerical calculations and the fitting of the Raman LOPC peak,we can obtain the carrier concentration excited by the laser,which will have certain significance to the further research of silicon carbide.