Abstract:

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 Ge doped SiC substrates have smaller lattice mismatch with III-nitride materials, which is beneficial to the reduction of dislocations density and the improvement of device performance.

Key words: physical vapor transport, Ge doping, SiC crystal, lattice parameters