ABSTRACT
Semiconductor materials are widely used in both optically and electrically pumped lasers. The use of semiconductor quantum-well (QW) structures as optical gain media has resulted in important advances in laser technology. QWs have a two-dimensional (2D), steplike density of electronic states that is nonzero at the band edge, enabling a higher concentration of carriers to contribute to the band-edge emission and leading to a reduced lasing threshold, improved temperature stability, and a narrower emission line. A further enhancement in the density of the band-edge states and an associated reduction in the lasing threshold is, in principle, possible using quantum wires and quantum dots (QDs) in which the confinement is in two and three dimensions, respectively. In very small dots, the spacing of the electronic states is much greater than the available thermal energy (strong confinement), inhibiting thermal depopulation of the lowest electronic states. This effect should result in a lasing threshold that is temperature insensitive at an excitation level of only one electron-hole (e-h) pair per dot on average [1,2]. Additionally, QDs in the strong confinement regime have an emission wavelength that is a pronounced function of size, adding the advantage of continuous spectral tunability over a wide energy range simply by changing the size of the dots.
