| In recent years, the search for novel structures for semiconductor lasers has proceeded primarily in two directions. The first direction is towards progressively greater quantum confinement of electrons in the active region. The second direction is towards reducing the number of optical modes within the gain bandwidth of the active medium and enhancing the interaction with electrons for selected optical modes by mode quantization in a microscopic cavity. In both cases, elementary analyses indicate substantial attendant improvements in the threshold current and the modulation bandwidth. This thesis explores the properties of quantum wire, quantum dot, and microcavity lasers from a rigorous theoretical perspective. In particular, the effects of band mixing in the valence band of lattice-matched and strained quantum wires, a finite carrier capture and thermalization time in the real quantum wire and dot structures, the peculiar photon density of states in an index-guided surface-emitting laser with submicron lateral dimensions, and the complicated interaction between the carriers in the compressively-strained quantum well active region and the quantized optical modes in the microcavity laser are considered in detail.;It is shown that the primary advantage of quantum wires is in the high differential gain that they are capable of providing, but not in the transparency current density. Furthermore, it is demonstrated that the thermalization time is increased by almost an order of magnitude in quantum wires and almost two orders of magnitude in quantum dots (if the structures with the best optoelectronic properties are considered) compared with quantum wells.;The degree of threshold reduction and its ultimate limits are examined for surface-emitting microcavity lasers. It is also shown that the modulation characteristics of practical microcavity lasers are not significantly different from those of more conventional semiconductor lasers. The spectral linewidth of the microcavity lasers is examined in a simple approximation, and it is shown that, although the linewidth may be broadened, it remains of the order of a gigahertz in well-designed microcavity lasers.;Finally, some of the applications of the novel semiconductor lasers are considered. A chirped pulse compression scheme with an exciton modulator is proposed. A wave propagation software is developed and demonstrated in the practical examples of semiconductor lasers with etched mirrors and optically controlled heterojunction bipolar transistors. |
