Strain relaxation was studied for the 10-period quantum-well heterostructures grown by MOVPE, In0.16Ga0.84N/GaN and In0.2Ga0.8N/GaN, both emitting with high efficiency in the blue and green regions, respectively. Additionally, a set of high-In content InGaN/GaN quantum-well structures, where growth parameters were kept constant but quantum-well numbers varied between 1 and 10, were also analyzed by transmission electron microscopy, X-ray diffraction and photoluminescence. For the highly-efficient green and the set of variable quantum-well samples, transmission electron microscopic structural studies identified large well-width fluctuations and misfit dislocations that threaded into the sample surface and were generated in the quantum well stack. This contrasted with similar observations of blue-emitting MQWs where misfit dislocations were not seen. Photoluminescence measurements were carried out for the In-rich quantum-well series and did not reveal a greater degradation of the optical properties with increasing numbers of quantum wells in the stack.

Misfit Dislocations in In-Rich InGaN/GaN Quantum Well Structures. P.M.F.J.Costa, R.Datta, M.J.Kappers, M.E.Vickers, C.J.Humphreys, D.M.Graham, P.Dawson, M.J.Godfrey, E.J.Thrush, J.T.Mullins: Physica Status Solidi A, 2006, 203[7], 1729-32