Observation of threading dislocations and misfit dislocation half-loops in GaN/AlGaN heterostructures grown on Si using electron channeling contrast imaging
Shizhao Fan, Rong Liu, Yingnan Huang, Jianxun Liu, Xiaoning Zhan, Xiujian Sun, Meixin Feng, Yuhao Yin, Qian Sun, Hui Yang
Abstract
We implemented invisibility criterion and black–white contrast orientation analysis into low-tilt electron channeling contrast imaging (ECCI) for dislocation-type discrimination in GaN and AlGaN layers grown on a Si(111) substrate. Our ECCI and x-ray diffraction (XRD) analysis attained consistent threading dislocation densities for GaN and AlGaN grown on Si, but demonstrated drastic discrepancy in the percentage of edge-type dislocations, potentially due to the lack of appropriate consideration of mixed-type (a→+c→) dislocations in XRD. Further ECCI analysis of GaN/AlGaN heterointerface revealed mixed-type (a→+c→) dislocation half-loops and dislocation bending due to compressive strain relaxation, validating that not all the dislocations originated from the mosaic or columnar structure. As a result, XRD analysis based on the mosaic block model does not give reliable edge-to-screw dislocation ratio. The observation of classic van der Merwe–Matthews-type dislocation half-loop nucleation and dislocation gliding could be associated with potential GaN/AlGaN optoelectronic device degradation issues.