Characterization of structure and defects in dot-in-well laser structures

Recent progress in the development of 1.3 μm InAs/InGaAs dots-in-a-well (DWELL) laser structures has led to efficient CW room temperature laser operation with low current thresholds. However, present devices suffer from non-ideal temperature characteristics due to gain saturation, a consequence of the finite dot density, and to carrier escape due to the small energy separation between the quantum dot (QD) ground and first-excited states. In order to improve device performance, we have examined methods to increase the QD quality and density. In these studies, we have examined the effect of using thin InAlAs capping layers and high temperature buffer layers. Both effects are observed to strongly modify the structure of the QDs producing significant improvements in the InAs QDs optical properties at room temperature. l attempts at multilayer QD structures showed substantial degradation in optical and electrical properties compared to single layer structures. Analysis by Transmission Electron Microscopy (TEM) has identified the presence of defects arising from the complex interaction of QDs, which propagate through the QD layers into the upper regions of the structure as being the primary cause of the poor electronic device characteristics. The use of high growth temperature spacing layers (HGTSLs) have recently allowed us the fabrication of a defect free five layer-stacked structure with record low threshold current density.