| Wide band gap semiconductor silicon carbide?SiC?has the characteristics of high thermal conductivity,high electron saturation drift velocity and large critical breakdown field strength.It has broad application prospects in high temperature,high frequency,high radiation,high power and so on.In addition,SiC can also form silica?SiO2?layer by oxidation.This feature makes SiC have the advantage that other wide band gap semiconductor materials do not have.However,the SiO2/SiC interface state density?Dit?by the method of traditional thermal oxidation is too high,which easily causes the threshold voltage of the device to drift,which makes the instability of the device properties and the decrease of the electronic mobility,the phenomena eventually lead to the reliability of the SiC MOS device greatly deteriorated.Therefore,building the SiO2/SiC interface and the defect model,exploring the passivation process of the SiO2/SiC interface and reducing the physical mechanism of the interface state are of great significance to the research of the SiC semiconductor?MOS?devices.Based on the density functional theory of first principles,the passivation mechanism of carbon dimer defects,which is an important defect of SiO2/SiC interface,is studied in this paper.Above all,we establish an amorphous SiO2/4H–SiC interface structure without defect.Then,two types of carbon dimers of O2-C=C-O2 and O2-?C=C?'-O2 were constructed in this interface.In order to passivate the defects,we study the carbon dimer defect structures passivation by H2.The results show that H2 can be adsorbed on O2–C=C–O2 defect to form a passivation structure,it converted the carbon–carbon double bond and remove the density of states?DOS?in the band gap,the result shows that H has a good passivation effect on O2–C=C–O2 defect.but H2 can not be adsorbed on O2–?C=C?'–O2 defect and can not passivate the defect.The effect of H2 passivation on SiO2/SiC interface was ineffective in the experiment,which can be explained by the H2 not being able to passivate all types of carbon dimer defects.Although there are different passivation processes,and the passivation structures obtained are also different.But NO can be adsorbed on the two types of defects,the ideal passivation effect is obtained by connecting some of the N–C bonds.The results of this study show that the key of passivation is transforming or breaking carbon–carbon double bonds.During the passivation process,some intermediate defects were produced,such as C2NO and O=C–C,which could contribute a defective DOS in the band gap of SiO2/4H–SiC interface.Such intermediate defects would seriously degrade passivation quality.Therefore,the defects of carbon dimer must be completely passivated during the passivation process to eliminate the density of defect states in the band gap completely. |
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