Silicon induced defect reduction in AlN template layers for epitaxial lateral overgrowth

The effect of Si doping on defect density in AlN layers grown on sapphire was analysed. Si concentration in the range of 1019 cm−3 leads to dislocation line inclination in AlN layers with a threading dislocation density of 3×1010 cm−2. Overgrowth of Si doped AlN layers by non-intentionally doped AlN results in a reduction of threading dislocation density by a factor of two. In contrast, an increase of the Si concentration to an order of 1020 cm−3 leads to a structural degradation of the AlN layers. The degradation process takes place through transformation to columnar-like growth. In a second experiment the AlN/AlN:Si/AlN layers with a decreased defect density were trench-patterned and used for subsequent epitaxial lateral overgrowth. In comparison to the epitaxial lateral overgrowth of non-intentionally doped AlN templates, the use of the AlN templates containing an AlN:Si interlayer allows to reduce the threading dislocation density in the defect-rich regions above the ridges in 6 µm thick epitaxial laterally overgrown AlN by a factor of 2.5.