Optical anisotropy induced by pyramidal defects in Mg-doped AlGaN∕GaN superlattices

Structural and optical properties of Mg-doped AlGaN∕GaN superlattices have been investigated by photoluminescence, scanning electron microscopy, cathodoluminescence (CL), and transmission electron microscopy (TEM). We found that the edge blue-band emission shows a strong optical anisotropy. Through the combination of the CL and TEM images, we clearly establish that the underlying microstructure responsible for the blue luminescence in Mg-doped AlGaN∕GaN arises from the pyramidal defects. The observed optical anisotropy is due to the well aligned pyramidal structure. Our result provides one of the model systems to demonstrate the correlation between optical transition and structural defect in a solid.