InAs/InGaAs/GaAs quantum dot lasers of 1.3 /spl mu/m range with enhanced optical gain

The need for long-wavelength cost-efficient GaAs-based lasers is currently a powerful driving force in the development of new GaAs-based heterostructures. 1.3-/spl mu/m lasers based on self-organized InAs quantum dots (QDs) embedded into InGaAs quantum well (QW) have demonstrated very low threshold current density (16 A/cm/sup 2/). On the other hand, low surface density of such QDs that provides the low transparency current density may also result in a small maximum optical gain on QD ground state. This motivated the use of low-loss cavity design (very ong cavities and/or HR/HR facet coatings), which is characterized by low external differential efficiency, /spl eta//sub D/, and output power. Previously the use of triply-stacked array of long-wavelength QDs allowed us to achieve /spl eta//sub D/ of 57% for edge-emitting lasers and realize 1.3-/spl mu/m VCSEL utilizing highly-reflective AlO/GaAs distributed Bragg reflectors. Further enhancement of optical gain of such QDs should improve efficiency of laser diodes as well as open new possibilities for their VCSEL application. However, increase in a number of QD planes, that results in corresponding increase of the saturated gain, typically led to degradation of threshold current and internal quantum efficiency of 1.3-/spl mu/m-QD lasers.