Nanoscale Lasers with Optical Microcavities.

Nanoscale lasers on silicon, defined by a confined modal volume less than a cubic wavelength in free space, have been attracting interest due to their possible application in on- and off-chip optical interconnects. This thesis is devoted to exploring different nanoscale coherent light sources with low threshold, which can be integrated with silicon technology. Silicon-based coherent light sources using colloidal PbSe quantum dots (QDs) embedded in photonic crystal (PC) microcavities were investigated. The room temperature photo- and electro-luminescence were enhanced by the PC microcavity at a wavelength of ~1.5μm accompanied by a linewidth reduction to ~4nm. The PbSe QDs were also sandwiched between metallic and distributed Bragg reflector (DBR) mirrors. Measured electroluminescence at room temperature showed coherent and directional emission at a wavelength of ~1.5μm with a linewidth of ~3nm. Optically pumped lasing from a monolithically integrated single GaN nanowire embedded in a PC microcavity on silicon was demonstrated. A single GaN nanowire is a favorable material to achieve nanoscale lasing due to its defect free nature and nanoscale dimensions. The PC microcavity device exhibited a lasing transition at λ=371.3 nm with a linewidth of 0.55nm and a modal volume of 0.003223μm3 (0.92(λ/n)3). A single GaN nanowire was also embedded in a dielectric microcavity with DBR mirrors to investigate optically pumped polariton lasing. Extremely low threshold polariton lasing, almost two orders of magnitude lower than previously reported values, was measured. Finally, a strain-driven rolled up microtube cavity with InAs QDs was studied. Rolled up microtubes provide a high quality factor due to their atomically smooth surface and near perfect overlap between the maximum optical field intensity and the QD layers. Optically pumped lasing from a free-standing microtube was demonstrated with multiple resonance peaks spaced apart by ~12meV with a pump threshold of ~700kW/cm2. Theoretical studies of the modal gain in a microtube were carried out to understand the effects of key design parameters, such as the tube diameter and wall thickness. The analysis reveals that the modal gain of this type of laser is inversely proportional to the radius of the microtube.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89735/1/jsheo_1.pd