Dielectric micro-cavity surface-emitting lasers

In recent years, various metal-cavity nano-lasers have been theoretically studied and experimentally realized because it is believed that their small sizes can actually bring large potential in the next-generation dense photonic integration and optical interconnects. However, the absorption loss in the metal fundamentally impedes the practical use of metal-cavity nano-lasers, as most of the demonstrated devices could only work either under optical pumping or at 77 K, except for the metal-cavity surface-emitting laser structure that came out from our group in 2010. In this thesis, the metallic cavity sidewalls in the previous design were replaced by dielectric material to reduce extra metal loss. Both theoretical and experimental studies on such dielectric micro-cavity surface-emitting lasers are presented. In addition, issues related to cavity size reduction are also investigated. A theoretical model, including the electronic band structure of the active material and the optical properties of the laser cavity, has been formulated to predict the working potential of the laser wafer, which was designed for actual fabrication. Lasing characteristics in devices having diameters ranging from 5 µm down to 2 µm have been demonstrated under continuous wave, electrical injection at room temperature. Threshold currents from devices with different diameters were collected for further study. The working devices generally had threshold currents around hundreds of µA, while their metal-cavity counterparts had previously-reported threshold currents in a few mA level. Such a two- to three-fold reduction in threshold current for a given device diameter can be attributed to the absence of metal absorption loss in the sidewalls, which is the major advantage of dielectric micro-cavity. Furthermore, besides the decrease of transverse optical confinement factor, the increase of threshold current density with the decrease of device diameter highlights the importance of controlling the sidewall roughness during fabrication