Shockley-Frank stacking faults in 6H-SiC

• We report on Shockley-Frank stacking faults (SFs) identified in 6H-SiC by a combination of low temperature photoluminescence (LTPL) and high resolution transmission electron microscopy (TEM). In the faulted area, stacking faults manifested as large photoluminescence emissions bands located in between the 6H-SiC signal (at ∼2.99 eV) and the 3C-SiC bulk-like one (at ∼2.39 eV). Each of the stacking fault related emission band had a four-fold structure coming from the TA, LA, TO, and LO phonon modes of 3C-SiC. Up to four different faults, with four different thickness of the 3C-SiC lamella, could be observed simultaneously within the extent of the laser excitation spot. From the energy of the momentum-conservative phonons, they were associated with excitonic energy gaps at Egx1 = 2.837 eV, Egx2 = 2.689 eV, Egx3 = 2.600 eV and Egx4 = 2.525 eV. In the same part where low temperature photoluminescence was performed, high resolution transmission electron microscopy measurements revealed stacking faults which, in terms of the Zhdanov notation, could be recognized as SFs (3, 4), (3, 5), (3, 6), (3, 7), (3, 9), (3, 11), (3, 16) and (3, 22), respectively. Among them stacking fault (3, 4) was the most common one, but a faulted region with a (4, 4) 8H-SiC like sequence was also found. Using a type II 6H/3C/6H quantum-well model and comparing with experimental results, we find that the photoluminescence emissions with excitonic band gaps at 2.837 eV (Egx1), 2.689 eV (Egx2), 2.600 eV (Egx3) and 2.525 eV (Egx4) come from SFs (3, 4), (3, 5), (3, 6) and (3, 7), respectively. A possible formation mechanism of these SFs is suggested, which involves a combination of Frank faults with Shockley ones. This provides a basic understanding of stacking faults in 6H-SiC and gives a rapid and non-destructive approach to identify SFs by low temperature photoluminescence.

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