Role of threading dislocations in strain relaxation during GaInN growth monitored by real-time X-ray reflectivity

Ga_1-xIn_xN epilayers (x = 0.09 or 0.14) grown on c-plane GaN layers with different densities of threading dislocations have been investigated by real-time x-ray reflectivity during metal-organic vapor phase epitaxial growth. We found that the density of pre-existing threading dislocations in GaN plays an important role in the strain relaxation of Ga_1-xIn_xN. Critical thicknesses were obtained and compared with theoretical predictions using the mechanical equilibrium model and the energy balance model. The critical thickness of GaInN varies inversely with dislocation density in the GaN sublayer. When the threading dislocation density in the sublayer was reduced by three orders of magnitude, the photoluminescence intensity of the Ga_0.86In_0.14N epilayer was improved by a factor of ten.