Bringing quantum dots up to speed [Breaking the phonon bottleneck with high-speed modulation of quantum-dot lasers]

In this article, we will focus on the carrier relaxation time in quantum dots (QDs), its probable mechanism, and the implications for the performance characteristics of directly modulated QD lasers and other QD devices. The electron and hole bound states and general predictions of carrier capture time into them will be presented, followed by a discussion of intersubband carrier relaxation in QDs. The modulation characteristics of QD lasers as a function of temperature will be described, and these modulation results will be discussed in terms of the temperature, composition, and size dependence of the relaxation time in QDs, including possible methods for designing QDs to overcome this relaxation time barrier. Also, the performance characteristics of other possible QD devices, such as intersubband lasers and detectors, will be examined in terms of our current understanding of the relaxation time in QDs.