High power continuous-wave operation of self-organized In(Ga)As/GaAs quantum dot lasers

Abstract

Quantum dot (QD) lasers are expected to have superior properties over conventional quantum well lasers due to a delta-function like density of states resulting from three dimensional quantum confinements. QD lasers can only be realized with significant improvements in uniformity of QDs free of defects and increasing QD density. In this paper, we first briefly give a review on the techniques for preparing QDs, and emphasis on strain induced self-organized quantum dot growth. Secondly, self-organized In(Ga)As/GaAs, InAlAs/GaAlAs and InAs/InAlAs QDs grown on both GaAs and InP substrates with different orientations by using MBE and the Stranski-Krastanow (SK) growth mode at our labs are presented. Under optimization of the growth conditions such as growth temperature, V/III ratio, the amount of InAs, In/sub x/Ga/sub 1-x/As, In/sub x/Al/sub 1-x/As coverage, the composition x, etc., controlling the thickness of the strained layers, for example, just slightly larger than the critical thickness and choosing the substrate orientation or patterned substrates as well, the sheet density of ODs can reach as high as 10/sup 11/ cm/sup -2/, and the dot size distribution is controlled to be less than 10%. These are very important to obtain a low threshold current density (J/sub th/) of the QD laser. How to improve the dot lateral ordering and the dot vertical alignment for realizing lasing from the ground states of the QDs and further reducing the J/sub th/ Of the QD lasers are also described in detail. Thirdly, based on the optimization of the hand engineering design for the QD laser and the structure geometry and growth conditions of QDs, 1 W continuous-wave (cw) laser operation of a single composite sheet or vertically coupled In(Ga)As quantum dots in a GaAs matrix and a larger than 10 W semiconductor laser module consisting of nineteen QD laser diodes is demonstrated. The lifetime of the QD laser with an emitting wavelength around 960 nm and 0.614 W cw operation at room temperature is over than 3000 hrs, at this point the output power was only reduced to 0.83 db. This is the best result as we know at the moment. Finally the future trends and perspectives of the QD laser are also discussed.