Microstructure of polycrystalline GaN grown on silica glass by ECR-MBE

We have investigated GaN grown on silica glass using TEM. Polycrystalline GaN grown without nitridation shows columnar structure with distributed growth orientation, in which threading dislocation density is relatively low. On the other hand, polycrystalline GaN grown with nitridation has columnar structure with uniform c-axis orientation. However, a high density of threading dislocation is observed.