Chapter 4 - Quantum Wire and Quantum Dot Lasers

Abstract

This chapter reviews the principles of quantum wire (QWR) and quantum dot (QD) lasers, and describes the recent developments in this field. It discusses the expected impact of the reduced dimensionality and quantum confinement on the optical properties of QWRs and QDs, the effects on semiconductor laser performance, and the special design issues applicable to these devices. The chapter also presents the state of the art of QWR and QD lasers, discussing the experimentally observed properties of wires and dots relevant to laser operation and comparing different designs, fabrication techniques, and performance. Quantum confinement of the charge carriers in more than one dimension in QWR and quantum dot QD heterostructures has been predicted to yield improved static and dynamic performance of semiconductor lasers as compared with quasi-two-dimensional (2D) quantum well (QW) devices. The integration of active regions composed of QWRs and/or QDs into the bulk laser diode structure offers both the advantage of the delocalized bulk electronic states, useful in the transport of the charge carriers to the recombination region, and the enhanced oscillator strength associated with the molecular- or atomic-like localized states in the wires or dots. A major challenge in this area has been the development of fabrication technologies for preparing QWR and QD heterostructures compatible with laser applications. Approaches for the realization of QWR and QD lasers fall into two general categories: techniques relying exclusively on postgrowth processing steps utilizing lithography for defining the wire and dot structures, and methods employing growth-related phenomena for creating the wire and dot potential wells.