Self-Consistent Calculation of Lasing Modes in a Planar Microcavity.

The vertical-cavity surface-emitting laser has attracted much attention recently due to its single-mode operation, small beam divergence, and low threshold current. Although there has been much progress in the process and design of this semiconductor laser, such lasers can exhibit complex transverse modes. In order to further improve the device performance, we need to investigate the physics of lasing action in this device. Therefore, in this dissertation, we present a self-consistent model for the calculation of lasing modes and their thresholds in the planar microcavities. First, with the semi-classical picture in which the emitter is treated as a two-state quantum system and light is treated as a classical electromagnetic wave, the stimulated emission is modeled as resulting from the polarization current sheet in the active region. Then self-consistency is imposed by requiring that the field generated by the polarization current must be the same field inducing polarization. With a finite gain profile, the calculated lasing modes along with their threshold show strong dependence on both cavity Q and the emitter distribution. The threshold for the lowest order mode initially decreases as the mode Q increases, and finally saturates due to the loss of spatial overlap between the driving field and the active region. We also present the calculated spontaneous emission characteristics in such planar microcavities. Our calculations show that almost 50% of the emission is coupled into the fundamental waveguide mode in a one-wavelength cavity. It is the cooperating effect of the distributed emitters that eliminates this strong waveguide coupling when the device is lasing. As the strong coupling is absent in a half -wavelength cavity, it is believed that the spontaneous emission factor is bigger in a half-wave microcavity.