Structural analysis of life tested 1.3 mu m quantum dot

We present the results of an accelerated life test study of quantum dot lasers operating at 1310 nm. The devices were run at 1 and 2 kA/cm(2) (similar to 10 and similar to 70 times I-th, depending on facet coatings), at temperatures of 80 and 100 degrees C for 1350 h. Some devices, particularly those with higher current densities, showed significant drops in output power and increase in threshold current over this time. The devices were examined using electroluminescence, which shows nonradiative recombination centers in the active region of the device as dark spots. A clear correlation between the density of dark spots and degradation is observed. The defect structure responsible for the dark spots has been identified using conventional and high-resolution cross-section transmission electron microscopy of selected structures. The defects consist of an inverted stacking fault pyramid or microtwin, enclosing the dot. The more extensive defects observed after the life test are consistent with their growth by climb, i.e., addition and/or removal of point defects. It is proposed that quantum dot devices show enhanced resistance to the growth of these defects in comparison with quantum well lasers. (c) 2008 American Institute of Physics.