Ultralow-threshold-current-density quantum dot lasers using the dots-in-a-well (DWELL) structure

Guangtian T. Liu, Andreas Stintz, Hua Li, Luke F. Lester, Kevin J. Malloy, Rolf H. Binder, Peter Blood, Marek Osinski
2000 Physics and Simulation of Optoelectronic Devices VIII  
Quantum dots laser diodes using the dots-in-a-well (DWELL) structure (InAs dots in an InGaAs quantum wells) have exhibited significant recent progress. With a single InAs dot layer in Inoi5Gao.8sAs quantum well, threshold current densities are as low as 26 A cm2 at 1 .25 xm. Quantum dot laser threshold current densities are now lower than any other reported semiconductor laser. In this work, the threshold current density is reduced to 1 6 A cm2 by HR coatings on the same device. Further
more » ... ce. Further investigation of performance reveals that use of multiple DWELL stacks improves the modal gain and internal quantum efficiency. It is suggested that carrier heating out of the quantum dots limits the T0 value of these DWELL lasers. ABSTRACT Theoretical study of threshold characteristics of a quantum dot (QD) laser in the presence of excited-state transitions is given. The effect of microscopic parameters (degeneracy factor and overlap integral for a transition) on the gain is discussed. An analytical equation for the gain spectrum is derived in an explicit form. Transformation of the gain spectrum with the injection current is analyzed. The threshold current density is calculated as a function of the total losses. The conditions for a smooth or step-like change in the lasing wavelength with the losses are formulated. Threshold characteristics of a laser based on self-assembled pyramidal InAs QDs in GaAs matrix are simulated. A small overlap integral for transitions in such QDs (and hence large spontaneous radiative lifetime) is shown to be a main possible reason for a low value of the maximum single-layer modal gain of the respective structure which is deficient to attain lasing at moderately short (several hundreds of micrometers) cavity lengths.
doi:10.1117/12.391490 fatcat:7cl3zdrrzbddxjwn7mkfgvn34a