| Semiconductor quantum dot lasers have an active medium that makes use three-dimensional quantum confinement effects and have been predicted to have many unique properties as compared to quantum well and double heterostructure lasers. In particular, they were expected to have low threshold current densities and temperature insensitive threshold currents.; In this dissertation, a new quantum dot laser structure called the "dots-in-a-well" (DWELL) laser, was successfully demonstrated and shown to have the lowest room temperature threshold current density (16 A cm-2) ever reported for any semiconductor laser. The internal efficiency, modal gain, and characteristic temperature of the DWELL lasers were systematically studied as a function of the DWELL-laser design parameters. It was noticed that the low modal gain of this and other quantum dot lasers is a factor limiting the performance of these devices. Different ways to improve the modal gain and characteristic temperature at the cost of higher threshold current densities are suggested. A quasi-equilibrium theory and rate equation model for the combined quantum well and quantum dot system are also used to investigate the properties of the DWELL structure. |
