Reduction of V-pit and threading dislocation density in InGaN/GaN heterostructures grown on cracked AlGaN templates

The high density of threading dislocations, often leading to the formation of inverted hexagonal pits in InGaN/GaN heterostructures on sapphire substrates, lowers the radiative efficiency of light emitting devices. In this study, a cracked AlGaN template has been implemented as a strain-relaxed layer for subsequent growth of InGaN/GaN heterostructures. The detailed electron microscopy and surface topographic analyses show that such a template has led to a reduction of threading dislocation density especially for screw dislocations and V-pits in the overgrown InGaN/GaN layers. The relaxed regrowth of such heterostructures also leads to an improved crystalline quality and a higher In incorporation in InGaN. The improvement in the optical and structural quality of these InGaN/GaN layers is investigated by means of photoluminescence spectroscopy and transmission electron microscopy.