堆垛层错对4H-SiC外延层少数载流子寿命的影响机理及表征方法研究

Minority carrier lifetime is seriously affected by the stacking fault in 4H-SiC epitaxial layer, which leading to the performance degradation of 4H-SiC bipolar device. However, the mechanism of stacking fault's impact on minority carrier lifetime is still unclear. In this project, both first principle calculation and experimental measurement are employed to investigate the mechanism and characterization method of stacking fault's impact on minority carrier lifetime of 4H-SiC. Firstly, considering the segregation of impurity at stacking fault, parameters of stacking fault (such as formation energy, defect energy level, density state and wave function etc.) are calculated by using first principle density functional theroy. Secondly, tip-enhanced Raman spectroscopy is used to determine the structure of stacking fault in 4H-SiC. Subsequently, by fitting longitudinal optical phonon-plasma coupled （LOPC）mode, carrier concentration at stacking fault is obtained, through which segregation degree of impurities at stacking fault is represented. Finally, in order to verify the accuracy of theoretical calculations, electron beam induced current method is adopted to measure the minority carrier lifetime at stacking fault. This project is of great significance not only to the growth of high-quality 4H-SiC material, but also to the fabrication of high-performance 4H-SiC bipolar devices.

4H-SiC外延层中的堆垛层错会严重影响材料的少数载流子（少子）寿命，进而导致4H-SiC双极器件的性能退化。但是，关于4H-SiC中堆垛层错对少子寿命的影响机理尚不清楚。本课题拟采用第一性原理计算与实验测定相结合的方法，系统研究4H-SiC中堆垛层错对少子寿命的影响机理及表征方法。首先，考虑杂质在堆垛层错处的偏聚效应，利用密度泛函理论计算堆垛层错的形成能、缺陷能级、态密度以及波函数等参数，并基于二阶微扰理论计算得到少子寿命。其次，利用针尖增强拉曼光谱技术确定4H-SiC中堆垛层错的结构，并通过拟和纵光学声子与等离子体激元耦合（LOPC）模得到堆垛层错处的载流子浓度，进而对杂质在堆垛层处的偏聚程度进行表征。最后，为了验证理论计算的准确性，采用电子束诱导电流法对堆垛层错处的少子寿命进行测量。本项目研究结果对生长高质量4H-SiC材料和制备高性能4H-SiC双极器件具有重要意义。

4H-SiC 外延层中的堆垛层错会严重影响材料的少数载流子（少子）寿命，进而导致4H-SiC 双极器件的性能退化。但是，关于4H-SiC 中堆垛层错对少子寿命的影响机理尚不清楚。本项目采用第一性原理计算与实验测定相结合的方法，系统研究4H-SiC 中堆垛层错对少子寿命的影响机理，此外，材料的少子寿命很容易受到温度效应的影响，因此在本项目的研究期间本人还针对无结晶体管器件的温度特性进行了分析。首先，通过工艺实验制备掺杂类型及掺杂浓度不同的堆垛层错样片，由于不同杂质在堆垛层错处的偏聚程度不同，会直接影响禁带中额外电子态的分布，进而进一步作为陷阱俘获载流子，造成少子寿命降低。本项目利用密度泛函理论的第一性原理计算并分析不同结构堆垛层错的形成能、缺陷能级、态密度以及波函数等参数，并基于二阶微扰理论计算得到其少子寿命的具体量值，并与实验结果做对比。其次，利用无损测试方法针尖增强拉曼光谱技术来确定纳米局域范围内4H-SiC 中堆垛层错的结构，并通过拟和纵光学声子与等离子体激元耦合（LOPC）模得到堆垛层错处的自由载流子浓度，进而对不同杂质在堆垛层错处的偏聚程度进行表征。由于宽禁带半导体材料SiC中存在典型的载流子冻析效应，同时，材料的少子寿命很容易受到温度效应的影响，而少子寿命的大小又会严重影响器件的电学特性。因此在本项目的研究期间本人还针对无结晶体管器件的温度特性进行了分析，获得了材料参数对器件电学特性的影响机制，为今后进一步研究SiC材料缺陷对器件电学特性的影响机制打下基础。本项目研究结果对生长高质量4H-SiC 材料和制备高性能4H-SiC 双极器件具有重要意义。