Intradot Relaxation of Carriers and Modulation Bandwidth in Quantum Dot Lasers With Double Asymmetric Barrier Layers

Electron-hole recombination outside of a quantum-confined active region presents a major challenge in conventional injection lasers. Double asymmetric barrier layers (DABLs) flanking the active region should efficiently suppress this parasitic recombination. One of the challenges still remaining in DABL lasers is the presence of excited states in the active region. In this work, the impact of such states in quantum dots (QDs) on static and dynamic characteristics of DABL QD lasers is examined. The most dramatic case is considered where carriers can only be captured into the QD excited state before decaying to the ground state and thus contributing to lasing. We show that there exist optimum values for the DC component of the injection current, QD surface density, and cavity length that maximize the laser modulation bandwidth. The maximum bandwidth itself is strongly controlled by intradot relaxation of carriers—while it remains almost unchanged at the excited-to-ground state relaxation times shorter than 0.01 ps, it drops considerably for longer relaxation times in the considered structures. A strict control of the parameters is thus essential in DABL QD lasers to increase their modulation bandwidth.