Study Of 4H-SiC Defect Evolution And Its Heterojunction Properties

With the vigorous development of 5G communications,new energy vehicles,aerospace,the nuclear power industry and other fields,the performance of traditional first-generation and second-generation semiconductor material devices such as silicon,germanium and gallium arsenide has been difficult to meet the needs of the industry.Silicon carbide as a representative of the third-generation semiconductor material has a series of advantages such as large bandgap,high breakdown voltage,high saturation electron drift velocity and high thermal conductivity,which has great potential in the field of electronic power devices.Among more than 250 types of SiC,4H-SiC has a high carrier saturation drift velocity(800～1000 cm²·V^-1·s^-1 for electrons),a wide bandgap（3.26 e V）,and a mature commercial production line.However,a large number of defects will be generated during the growth of the 4H-SiC single crystal.On the one hand,it will lead to a decrease in the yield of SiC wafers,which will make the cost too high;on the other hand,it will make it difficult to achieve the ideal performance of SiC-based devices.In order to study the defects in 4H-SiC,this thesis investigated the relationship between different types of 4H-SiC and etching conditions by chemical etching and makes a statistics and summary.Then we studied the irradiation effect of 4H-SiC material by ion irradiation and characterized the structural changes and defect behaviors of the 4H-SiC under different irradiation conditions.Finally,a new monolayer MoS₂/4H-SiC heterostructure was designed and prepared by theoretical calculations and experiments,and the band alignment of the heterojunction was measured by XPS spectroscopy.The main research contents are as follows:1.The chemical mechanism of KOH etching of SiC crystals was studied,and the etching morphology of N-type SiC single crystal samples,semi-insulated SiC single crystal samples,and N-type SiC epitaxial samples were observed and summarized by different etching temperatures,etching times,and catalyst types to obtain a suitable experimental condition and observation results.We propose a method for the rapid differentiation of threading screw dislocation（TSD）and threading edge dislocation（TED）on 4H-SiC single crystals in the dark field and summarize the relationship between the change of basal plane dislocation（BPD）morphology and the off-angle and crystal orientation of SiC samples.2.The 4H-SiC single crystal sample was irradiated with Xe ions and Ta ions using the Lanzhou Heavy Ion Accelerator facility at the Institute of Modern Physics,Chinese Academy of Sciences,and the surface morphology and chemical composition of the sample were studied before and after irradiation using chemical etching,Raman spectroscopy,photoluminescence spectroscopy and XPS spectroscopy.The research results show that Xe ions with low irradiation energy and Ta ions with high irradiation energy have different damage ranges in 4H-SiC,but both can cause the Si-C bond in SiC to break,forming C antisite defects,Si antisite defects and C vacancy defects and its complexes.With the increase of irradiation fluence,the degree of disorder in SiC crystal increases,and at 2×10¹⁵ cm^-2,the SiC surface area reaches the threshold of amorphization.3.The structural and electronic properties of monolayer MoS₂/4H-SiC（Si-face）heterojunctions are systematically investigated through density functional theory calculation and experimental analysis.The calculated results show that the monolayer MoS₂/4H-SiC heterostructure is a van der Waals heterojunction because of low formation energy and shows a type-II band alignment with a valence band offset of 1.43e V.Then,we obtained a high-quality vd W MoS₂/4H-SiC heterojunction by the wet transfer technique and measured it by X-ray photoelectron spectroscopy.The monolayer MoS₂/4H-SiC heterojunction has a type-II band alignment and the VBO is1.87 e V,which is in agreement with our calculated results.This kind of heterostructure has excellent electron–hole pair separation ability,which means it has great development potential in the field of photocatalysis and energy conversion.