Epitaxial layers threading dislocations

Bulk plate shaped GaN crystals do not have threading dislocations along the c-axis which would end at the (0001) surfaces. This is very different in comparison with GaN layer crystals grown on any substrate. It is also important with respect to application of these plates as substrates for homoepitaxial growth, since threading dislocations in a substrate propagate into the epitaxial layers. 

In order to produce SiC material of the level of quality required for device applications, chemical vapor deposition (CVD) is currently used as the primary growth technique for SiC epitaxy [2], Due to the continuous improvements in commercial substrate quality, the presence of micropipes in SiC epilayers is not the device yield limiting issue as it was a decade ago. However, the epitaxially grown SiC films still suffer from other extended defects such as basal plane and threading edge dislocations as well as point defects. The vision of growing SiC on porous SiC was to reduce the concentration of these defects and thus improve the epitaxial layer quality for device applications. 

The threading dislocations in the epitaxial layer on Si substrate are classified into (1) dislocations that originate from the dislocations in the Si substrate,... 

Freund, L. B. (1990), A criterion for arrest of a threading dislocation in a strained epitaxial layer due to an interface misfit dislocation in its path. Journal of Applied Physics 68, 2073-2080. 

Zhu et al. (1990) report epitaxial microstructures characterized by HREM and RBS. It is observed that ErAs can have an excellent epitaxy on (100) GaAs substrates. On the other hand the overgrown GaAs layer can present twins, threading dislocations (for thick ErAs layers), different epitaxial orientations (such as (111) GaAs on (100) ErAs)... 

Figure 7.19 A transmission electron micrograph looking down upon the interface between a GaAs substrate and an InAs epitaxial layer. Both threading segments stretching from the heterojunction to the surface and reactions between dislocation segments are visible in the micrograph. The lines in the image are the misfit dislocations in the interface. [8]...

---