High-performance 1300-nm InAs/GaAs quantum-dot lasers

Abstract

Quantum dot (QD) lasers incorporating the dot-in-a-well (DWELL) structures offer the prospect of lowcost and high-performance sources for telecom applications at 1300 nm. A number of significant advantages have been demonstrated to arise from the 0-D density of states, such as low threshold, low noise, low chirp and relative temperature insensitivity. However QD lasers suffer from a low modal gain per dot layer, which is a major factor of limiting high-speed performance. To address this, both a high inplane dot density and the use of multilayer structure are necessary and this presents a major challenge for molecular beam epitaxy (MBE) growth. In this work, to increase the gain of 1300-nm quantum-dot (QD) lasers, we first optimize the MBE growth of InAs/InGaAs QD structure for single-layer epitaxy structure with In composition within InGaAs well. Then we proposed a growth technique, high-growthtemperature spacer layer to suppress the dislocation formation for the multilayer QD structure. These lead to the realization of high-performance multilayer 1300-nm QD lasers with extremely low threshold current density (Jth) of 17 A/cm2 at room temperature (RT) under continuous-wave (cw) operation and high output power of over 100 mW. By combining the high-growth-temperature spacer layer technique with the p-type modulation doping structure, a negative characteristic temperature above RT has been demonstrated for a 5-layer QD laser structure. Further modification of the high-growth-temperature spacer layer technique, we realized a very low RT threshold current density of 33 A/cm2 for a 7-layer ptype- modulated QD laser. The temperature coefficient of ~0.11 nm/K over the temperature range from 20 to 130 °C has also been realized by modifying the strain profile of InGaAs capping layer. These techniques could find application in lasers designed for optical fiber systems.