Study Of Raman Scattering In 4H-SIC Homogeneity Epitaxial Material

As the representative of the third generation wide band gap semiconductor materials,the silicon carbide(SiC)materials have the advantages of large band gap,high thermal conductivity,high electronic saturation rate and high breakdown electric field.It has an irreplaceable advantage in the fields of high temperature,high voltage,high frequency,high power electronic devices,and aerospace,military,nuclear and other polar environment applications.It is still a hot topic in the research of semiconductor materials.The quality of silicon carbide materials' epitaxial layer has an important influence on device fabrication and performance.There are lattice mismatch and internal defects in heteroepitaxial growth of silicon carbide materials,which limits the application of power semiconductor devices.The silicon carbide materials grown by homogeneous epitaxy can better improve this situation.But the epitaxial layer quality analysis is difficult because the epitaxial layer and substrate of the 4H-SiC materials are homogeneous materials.In this paper,the crystal mass and carrier properties of a series of 4H-SiC films with homogeneous epitaxial are studied by multi-wavelength UV and cross section Raman scattering spectra.In addition,the anisotropy of 4H-SiC material was studied by polarized Raman spectroscopy.The main research contents of this article are as follows:(1)The quality characteristics of the surface layer,middle layer and the whole epitaxial layer of the homogeneous epitaxy 4H-SiC films with different silicon carbon ratio were analyzed by using 266nm,325nm and 514nm laser excitation and the penetration properties of different wavelengths of UV laser.By using the commonly used taboo mode Ei(TO)characteristic and the spatial correlation model,the crystal quality information of each layer of the sample was obtained.It was shown that taboo mode Ei(TO)was sensitive to crystal quality and it's also a good quality probe.(2)Section Raman scattering spectroscopy were used to study the carrier characteristics of different crystal layers in the homogeneous epitaxiy undoped 4H-SiC/n+ 4H-SiC sample.In this study,there was no obvious change in the peak and peak intensity of Raman A1(LA),E2(TO)and A1(LO)modes along the direction of growth.And it showed that the concentration of different impurities had little effect on the E2 and Ai modes.However,the peak and peak intensity of the LOPC modes at different positions were different for the LOPC mode.By comparing the linear change of the LOPC mode,the carrier concentration change properties of the samples along the growth direction were obtained.(3)The anisotropy of 4H-SiC was studied by means of variable angle polarized Raman scattering spectrum and phonon dispersion relation.The relationship between the polarization components of A1,E2 and E1 modes and the angle theta of scattered light was obtained when the angle between the polarization of incident light and the optical axis of the crystal changed.According to the Raman selection rule,the values of each Raman tensor element of A1,E1 and E2 modules were obtained by fitting analysis.And their anisotropy characteristics were also analyzed.