Effects of photon and thermal coupling mechanisms on the characteristics of self-assembledInAs∕GaAsquantum dot lasers

Abstract

The relative contributions of the photon and thermal coupling mechanisms to the behavior of self-assembled $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot lasers are studied. A theoretical model, which takes into account a photon coupling process between the ground and first excited states of different sized dots, is proposed to fully explain the temperature dependence of the threshold current density $({J}_{\mathrm{th}})$ of both undoped and $p$-doped lasers. The simulation results suggest that the carrier distribution between the different energy states in a dot is modulated by the intradot thermal excitation of carriers. This process, when combined with the photon coupling mechanism, can account for the negative characteristic temperature $({T}_{0})$ appearing in different temperature ranges for undoped and $p$-doped devices. Thermal coupling, which involves thermal carrier escape and recapture among different dots, has also been studied. Below threshold, thermal coupling is found to be significant but is weakened as threshold is approached because of the decreased carrier lifetime. Near and above threshold, the photon coupling mechanism is important and can be used to model the different temperature behaviors of the lasing spectra observed experimentally for the undoped and $p$-doped lasers.