TEM Study on Microstructure of Stacking Fault Nucleation Sites in 4H-SiC P-I-N Diodes

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Silicon carbide(SiC) is an attractive material for high-power applications. However, a number of crystal defects in SiC substrates and epitaxial layers limit commercialization of SiC-based devices. For example, the expansion of Shockley-type stacking faults(SFs) produced by dissociation of basal plane dislocations(BPDs) in 4H-SiC epitaxial layers cause the degradation(forward voltage drop) of p-i-n diodes under forward bias. Since it has been found that the nucleation sites of SFs are pre-existing BPDs, it is necessary to eliminate the BPDs in epitaxial layers. There are two types of nucleation sites of the SFs in different shapes. One is the “line source”, and the other is the “point source”. The line source is the basal plane screw dislocations which parallel to the off cut direction with Burgers vector 1/3[11-20] in the epitaxial layers. Their shape can be clearly observed by electroluminescence or X-ray topography as a straight line. On the other hand, the dislocation structure of the point source is not well known. To eliminate the point source of the SFs, it is necessary to know more about microstructure of their nucleation sites and origin. In this work, we investigated the microstructure of the “point source” and its origin in p-i-n diodes using photoluminescence imaging and transmission electron microscopy. As a result, we found a short basal plane screw dislocation segment(about 300 nm) along [-12-10] direction at the nucleation site of the SF located on a little above the epilayer/substrate interface. The BPD segment was converted from a part of the threading edge dislocation(TED). The TED/BPD/TED structure would be formed during epitaxial growth or subsequent thermal treatment.