I. Magnusdottir

Ultrafast gain recovery and modulation limitations in self-assembled quantum-dot devices

Measurements of ultrafast gain recovery in self-assembled InAs quantum-dot (QD) amplifiers are explained by a comprehensive numerical model. The QD excited state carriers are found to act as a reservoir for the optically active ground state carriers resulting in an ultrafast gain recovery as long as the excited state is well populated. However, when pulses are injected into the device at high-repetition frequencies, the response of a QD amplifier is found to be limited by the wetting-layer dynamics.

Line broadening caused by Coulomb carrier–carrier correlations and dynamics of carrier capture and emission in quantum dots

Mechanisms of pure dephasing in quantum dots due to Coulomb correlations and the dynamics of carrier capture and emission are suggested, and a phenomenological model for the dephasing is developed. It is shown that, if the rates of these capture and emission processes are sufficiently high, significant homogeneous line broadening of the order of several meV can result.

One- and two-phonon capture processes in quantum dots

Multiphonon capture processes are investigated theoretically and found to contribute efficiently to the carrier injection into quantum dots. It is shown that two-phonon capture contributes where single-phonon capture is energetically inhibited and can lead to electron capture times of a few picoseconds at room temperature and carrier densities of 1017 cm−3 in the barrier.

Influence of quasibound states on the carrier capture in quantum dots

The interaction of carriers in quantum-dot quasibound states with longitudinal optical phonons is investigated. For a level separation between the quasibound state and a discrete quantum-dot state in the vicinity of the phonon energy, a strong electron–phonon coupling occurs. A mixed electron–phonon mode—polaron—is formed. The finite lifetime of the phonons is shown to give rise to another type of carrier capture into quantum dots.

Gain recovery dynamics and limitations in quantum dot amplifiers

Summary form only given. While ultra-low threshold current densities have been achieved in quantum dot (QD) lasers, the predicted potential for high-speed modulation has not yet been realized despite the high differential gain. Furthermore, recent single pulse experiments demonstrated very fast gain recovery in a quantum dot amplifier, and it is thus not yet clear what the limiting processes for the device response are. We present the results of a comprehensive theoretical model, which agrees well with the experimental results, and indicates the importance of slow recovery of higher energy levels. The model used is of the rate-equation type with three energy levels: ground state (GS) and excited state (ES) dot levels and a wetting layer.

Two-phonon capture processes into quantum dots: the role of intermediate states

Abstract We present a study of carrier capture into quantum dots via emission of longitudinal optical phonons. Two-phonon capture times are found to be of the order of some picoseconds at carrier densities 10 17 cm −3 in situations where single-phonon capture processes are energetically prohibited. The influence of different intermediate carrier states on the two-phonon capture rate is investigated and found to exhibit effects of interference between the different contributions.

Temperature characteristics of quantum dot devices: Rate versus Master Equation Models

The change of transparency current with temperature for quantum dot devices depends strongly on whether a rate or master equation model is used. The master equation model successfully explains experimental observations of negative characteristic temperatures.