Effect of excited states on the ground-state modulation bandwidth in quantum dot lasers

Abstract

We consider direct and indirect (excited-state-mediated) capture of carriers from the waveguide region into the lasing ground state in quantum dots (QDs) and calculate the modulation response of a QD laser. We show that, when only indirect capture is involved, the excited-to-ground-state relaxation delay strongly limits the ground-state modulation bandwidth of the laser—at the longest tolerable relaxation time, the bandwidth becomes zero. When direct capture is also involved, the effect of excited-to-ground-state relaxation is less significant and the modulation bandwidth is considerably higher.

Ground-state modulation-enhancement by two-state lasing in quantum-dot laser devices

“…Modulation bandwidths are also strongly dependent on the scattering scheme, as was reported in Ref. 12. The authors found indirect, ES-mediated capture processes to be detrimental to GS bandwidth.…”

“…[6][7][8] Nonetheless, due to their low threshold currents, high temperature stability, and high efficiency, 9 studying their dynamic properties is still the topic of many recent publications. 1,[10][11][12][13] Moreover, QDs also exhibit some unique lasing behavior, setting them apart from other gain materials. Because of their effectively zero-dimensional structure, electronic states are quantized in a quasi-atom-like fashion, giving rise to multiple well separated energy levels.…”

“…[19][20][21][22] In this paper, we study the interplay of two-state lasing and modulation capabilities. We go beyond studying only the effect of the excited states on the carrier lifetimes [10][11][12] by also considering the effect of ES lasing, i.e., on the large and small-signal modulation response of the GS. To be able to correctly predict the performance, we use a microscopically motivated multi-level rate-equation model with stochastic spontaneous emission noise, which separately treats electron and hole dynamics.…”

Спектроскопия возбуждения фотолюминесценции массивов квантовых точек InAs/InGaAs/GaAs в температурном диапазоне 20-300 K

“…В КТ достаточно большого размера существует значительное количество электронных и дырочных уровней, которые формально могут соответствовать большому количеству возбужденных состояний [14]. Однако вероятность перехода с большинства этих возбужденных состояний на основанное состояние довольно мала [15] вследствие правил отбора. В то же время интенсивность пика возбужденного состояния может значительно возрастать, если его энергия отстоит от энергии основного состояния на кратное число LO-фононов, что значительно облегчает релаксацию носителей.…”

Dynamic characteristics of two-state lasing quantum dot lasers under large signal modulation

“…For the theoretical model used in the study, three states including GS, ES, and wetting layer (WL) are considered in the QD laser. 15,17,18 It is assumed that the downward carriers in the WL can be either directly captured into the GS or excited-state-mediated. The carriers also can escape back to the WL via those two ways.…”