Optical Science and Engineering ETDs


Changyi Li

Publication Date



III-nitride nanowire lasers have drawn significant attention as potential compact coherent light sources for a wide range of applications such as on-chip communication, optical sensing, and solid-state lighting. For practical applications, control over the lasing properties is needed. For example, a single mode lasing is beneficial for reducing the pulse broadening and the signal errors during the optical communications. An annular-shaped beam could be potentially used for the atom trapping or the stimulated emission depletion spectroscopy. The polarization-sensitive on-chip optical components also require linear polarization. However, due to the compact size of nanowire lasers and the cross-sectional symmetry of the traditional nanowire lasers, controlling the lasing properties still remains challenging. A top-down two-step etch process developed for vertical GaN nanowires offers the ability to precisely control the cross-section of the nanowire lasers. Consequently, the lasing properties can potentially be tailored by controlling the cross-section. In this dissertation, annular-shaped emission was demonstrated from GaN nanotube lasers with optical pumping at room temperature, consistent with finite-difference time-domain simulation results. Linearly polarized lasing emission was also realized from rectangular cross-sectioned GaN nanowire lasers. When the shorter y-dimension is ~120 nm, the rectangular cross-section creates a large contrast of the effective index of refraction, resulting in higher transverse confinement factors for the y-polarized modes than for the x-polarized modes. In order to pursue electrically injected single III-nitride nanowire lasers, non-polar InGaN/GaN multi-quantum-wells core-shell nanowires were fabricated by a combination of the top-down two-step etch process and a regrowth process. Lasing was observed from the core-shell nanowires by optical pumping at room temperature. A Hakki-Paoli measurement shows high modal gains of the non-polar core-shell nanowire lasers and the non-uniform gains resulting from the inhomogeneous regrowth. As a step towards electrical pumping, a Ti ohmic like' contact to the n-GaN core was fabricated. However, because of the lack of the ohmic contact to the p-GaN shell, the injection efficiency was extremely limited. As a result, instead of electrically-driven lasing, only weak spontaneous emission was observed in the electroluminescence measurement.'

Degree Name

Optical Science and Engineering

Level of Degree


Department Name

Optical Science and Engineering

First Advisor

Brueck, Steven

First Committee Member (Chair)

Brueck, Steven

Second Committee Member

Wang, George

Third Committee Member

Feezell, Daniel

Fourth Committee Member

Dawson, Ralph

Fifth Committee Member

Ganesh, Balakrishnan

Document Type