3.1 INTRODUCTION

During the last decade there has been increasing interest in semiconductor quantum nanostructures, including quantum wires and quantum dots (QDs), due to their unique optical properties. The additional quantum confinement in a wire or dot concentrates the density of states into a narrower energy range at the subband edges in quantum wires and into a series of discrete states for quantum dots. This concentration of the density of states greatly enhances the optical response of the nanosystem because more optical transitions are active at nearly the same energy, opening the possibility, for example, to engineer nanoscale lasers with greatly enhanced performance. Quantum dots, with their discrete electronic energy levels, are uniquely different from higher dimensional quantum structures, such as quantum wires and quantum wells. In principle, quantum dots behave as artificial atoms with their linear and nonlinear optical response governed by the physics of discrete levels and transitions. This provides the promise of exquisite control over optical processes because specific transitions can be pumped and manipulated with interlevel relaxation hindered by the discrete spacing of levels. Just as importantly, these properties of the quantum dots can be tailored by controlling the size, shape, and composition of the QDs. Moreover, QDs can be fabricated directly in semiconductor device structures, providing a way to engineer and exploit these nanostructures and their unique optical properties in fully integrated optical and optoelectronic devices.

Great progress has been made toward...