Ge掺杂碳化硅晶体的生长缺陷

Defects in Ge Doped SiC Crystals

采用物理气相传输法(PVT)制备了2英寸Ge掺杂和非掺SiC晶体,并使用二次离子质谱仪(SIMS)、显微拉曼光谱(Raman spectra)仪、体式显微镜、激光共聚焦显微镜(LEXT)和高分辨X射线衍射(HRXRD)仪等测试手段对其进行了表征。结果表明,Ge元素可以有效地掺入SiC晶体材料中,且掺杂浓度达到2.52′1018/cm3,伴随生长过程中Ge组份的消耗和泄漏,掺杂浓度逐渐降低;生长初期高浓度Ge掺杂会促使6H-SiC向15R-SiC晶型转化,并随着生长过程中Ge浓度的降低快速地转回6H-SiC稳定生长。用LEXT显微镜观察发现,生长初期过高的Ge掺杂导致空洞明显增多,位错密度增加,掺杂晶体中位错密度较非掺晶体增大一倍。HRXRD分析表明掺Ge能增大SiC晶格常数,这将有利于提高与外延III族氮化物材料适配度,并改善器件的性能。

2-inch Ge doped and undoped SiC crystals were grown by physical vapor transport （PVT） method and characterized by secondary ion mass spectrometry （SIMS）, Raman spectroscopy, stereomicroscope, laser scanning confocal microscope （LEXT）, high resolution X-ray diffractometry （HRXRD）. The experimental results showed that the element Ge was effectively doped into 6H-SiC crystal with doping level reaching up to 2.52× 1018/cm3. Following crystal growth, the Ge concentration in crystal gradually dropped due to impurity source depletion and leakage. Raman mapping clearly shows that the excessive Ge doping can cause SiC polytype structure transformation from 6H-SiC into 15R-SiC at the initial crystal growth stage and then rapidly transform from 15R-SiC back into 6H-SiC following the Ge concentration reduction in the growth process. Microscopic observation indicates that the excessive Ge doping at initial growth stage results in the increase of hollow density and the multiply of dislocation. And the dislocation density in doped crystal is almost two-fold of that in undoped crystal. HRXRD pattern demonstrates that the lattice parameters in Ge doped SiC crystal are enlarged because of a longer atomic bonds caused by Ge doping. Therefore, the Gc doped SiC substrates have smaller lattice mismatch with III-nitridc materials, which is beneficial to the reduc- tion of dislocations density and the improvement of device performance.