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Title: Design and fabrication concepts for nanolasers
Author: Kastein, Lewis
ISNI:       0000 0004 5919 8154
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2015
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This thesis investigated the design and fabrication of three nanodevices, a hybrid-plasmonic device, an InP composite pillar-polymer device, and a GaN composite pillar-polymer device. The hybrid plasmonic device consists of a gain material separated from a metal stripe layer by a dielectric layer. The optical mode within the gain material becomes bound to the metal region and hybridises with surface plasmon oscillations, resulting in Ohmic absorption losses. The dielectric gap is used to reduce Ohmic absorption losses. A Fabry-Perot cavity can be formed by reflections from the edges of the metal stripe. Aspects of the device were investigated, including its fabrication, the importance of the alignment of smaller structures to larger structures, and contact metallisation. A more detailed study was carried out on the fabrication of two aspects of the device, the semiconductor slab thickness and dielectric gap thickness. For this device a TM emitting 633nm laser structure was designed to provide gain, the characteristics of the grown wafer were confirmed using edge photovoltage spectroscopy, showing that the electron to light hole transition was at a lower energy than the electron to heavy hole transition, and existed at a wavelength of 633nm. A strong dependence of loss with the semiconductor slab thickness and dielectric gap thickness was calculated. A single nanometer change in the dielectric gap thickness can alter the mode cut-off by a semiconductor slab thickness of up to 100nm, and can change the mode loss up to 600cm-1. In addition, the mode is pulled towards the metal/dielectric region, resulting in a small optical confinement factor in the central quantum well region, and a low modal gain that can not compensate losses. A high energy density was modelled within the dielectric layer, and the mode was found to be bound to the metal region, which may be useful for some applications. Fabrication of a nanosquare device with electrical injection was investigated, the importance of alignment procedures were noted and metallisation was explored. The specific contact resisitivity of the contacts was found to be in the order of, or better than, similar fabricated contacts, found to be 3 x 10-3 ohms.cm2 and 4x10-6 ohms.cm2 for the p and n type contacts respectively. However, the small injection mesa suffered from heating and resulted in contact metal delamination. An alternative injection method using current apertures was presented, and fabrication of aspects of the design were explored.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics