7.1 INTRODUCTION

Semiconductor lasers operating due to recombination of charge carriers confined to quasi one- (1D) and zero-dimensional (0D) quantum wires (QWRs) and dots (QDs) have been a challenge to the photonics field for more than a decade. Just as the two-dimensional (2D) quantum well (QW) lasers have replaced bulk three-dimensional (3D) semiconductor devices due to their superior performance, further improvements in threshold current, differential gain, as well as reduced sensitivity of threshold current and emission wavelength to ambient temperature, are expected from 1D and 0D lasers [1 3]. The reduction in threshold current is a direct consequence of the smaller volume of optically active material in lower dimensional lasers. In addition, the 1/ as well as the ?-function singularities in the density of states (DOS) at the band edge of 1D and 0D systems, respectively, as opposed to the square root and step-like DOS profiles in 3D and 2D, should lead to enhanced optical nonlinearities [4], narrower optical gain spectra, and higher differential gain [2]. Furthermore, increased exciton binding [5, 6], anomalously strong concentration of the oscillator strength at the lowest-energy exciton state [7], and exciton condensation [8] are predicted as a result of Coulomb interaction in such strongly confined electron-hole systems.

The breakthrough of 2D semiconductor systems for optical and transport applications like the intersubband detector or the high electron mobility transistor was triggered by...