Effect of Boron Incorporation on Structural and Optical Properties of AlN Layers Grown by Metal-Organic Vapor Phase Epitaxy

To investigate the effect of boron (B) incorporation on the structural and optical properties of aluminum nitride (AlN) layers, B-doped AlN layers without columnar structures are grown on c-plane sapphire substrates with an AlN underlayer by metal-organic vapor phase epitaxy. Triethylboron, trimethylaluminum, and ammonia are used as B, Al, and N precursors, respectively. The B-doped AlN layers exhibit a homogeneous B concentration of 2.0 x 10(21) cm(-3) (approximate to 2%) at the macroscale and microscale. However, most of the B atoms segregate in the AlN layer at the nanoscale and do not form BAlN alloys. As a result, high-density dot-shaped crystalline defects are induced in the layer. The dot-shaped crystalline defects align along the {112 over bar 3} facets and form complex inclined defects with high-density oxygen atoms. These defects result in much worse crystalline quality and optical emission property than those of conventional crystalline defects, e.g., threading dislocations and stacking faults. Therefore, further improvement in the crystalline quality of B-doped AlN is important to understand the potential properties of BAlN alloy semiconductors.