A combination of techniques was used to characterize low defect-density (less than 105/cm2) heterostructure lasers. The limits of lattice mismatch, between substrate and quaternary cladding layer, that resulted in a pseudomorphic laser structure were deduced (by means of X-ray diffraction and transmission electron microscopy) to be less than 0.0015. Measurements of defect (stacking faults, threading dislocations) density in the active layer were performed by using optical imaging techniques. It was noted that photoluminescence imaging was suitable for defect observation, because of the non-radiative transitions that were associated with the defects, and could be easily applied to large areas. The propagation of defects during device operation was monitored in real time by means of optical imaging. The degradation was observed to start from grown-in defect sites, in the active layer, that originated from (100) dark-line defects. A mechanism was proposed that involved the creation of new defects from non-radiative recombination at existing defect sites.

J.Petruzzello, K.W.Haberern, S.P.Herko, T.Marshall, J.M.Gaines, S.Guha, G.D.U’Ren, G.M.Haugen: Journal of Crystal Growth, 1996, 159, 573-81