Characterization of low defect density blue-green lasers

Abstract

We have used a combination of techniques to characterize low defect density (≤ 105 cm-2) blue-green separate confinement heterostructure lasers. The limits of lattice mismatch between the substrate and quaternary cladding layers that result in a pseudomorphic laser structure were determined by X-ray diffraction and transmission electron microscopy to be ≤ 0.0015. The determination of defect density (stacking faults, threading dislocations, etc.) in the active layer was performed by optical imaging. Photoluminescence imaging is nicely suited for defect observation, because of the nonradiative transitions associated with the defects and can easily be performed over large areas. Propagation of defects during device operation (device degradation) was monitored in real time with optical imaging. The degradation was observed to start at grown-in defect sites (in the active layer) that emanate from (100) dark line defects. From the direct observation of device degradation, a mechanism involving the creation of new defects from nonradiative recombination at existing defects sites is proposed.