Optical Science and Engineering ETDs

Publication Date

Spring 5-15-2019


GaN nanowires are promising for optical and optoelectronic applications because of their waveguiding properties and large optical bandgap. Recent researches have shown superior mechanical properties of GaN nanowires which promises their use in new research areas e.g. nanometrology. In this work, we develop a scalable two-step top-down approach using interferometric lithography as well a bottom-up growth of NWs using MOCVD, to manufacture highly-ordered arrays of nanowires with atomic surface roughness and desired aspect-ratios to be used in nanophotonics and atomic precision metrology and lithography. Using this method, uniform nanowire arrays were achieved over large-areas (~1 mm2) with aspect-ratio as large as 50, radius as small as 17 nm. The mechanisms involved in the wet-etch process are thoroughly investigated and FDTD modeling is employed to study modal properties of the fabricated GaN NWs. It is shown that HE11 is the dominant transverse mode in the nanowires with sub-100 nm radius. Single-mode lasing with high Q-factors of ~1139-2443 were obtained in nanowire array lasers, corresponding to a linewidth of 0.32-0.15 nm. We also demonstrate the preliminary result of including nanoporous AlxGa1-xN DBRs in the GaN nanowire structures grown on Si, not only to enhance modal reflectivity, but also to alleviate accumulating tensile stress due to the lattice and thermal expansion constants mismatch between overgrown GaN and Si.

Top-down fabricated GaN NWs and sharp bottom-up grown GaN NWs were used to fabricate AFM and STM tips for nanometrology. The advantages of these tips are to assist nanometrology in scanning high-aspect-ratio structures, provide cost-effective and durable tips for scanning probe lithography for the creation of sub-10 nm features, and enabling tip-based nanometrology with Raman spectroscopy. GaN NWs as a new material for AFM tips, enhanced image resolution in scanning high-aspect-ratio structures with straight sidewalls. Using sharp GaN NWs as STM tips, we could demonstrate atomic resolution imaging and sub-10 nm lithography with a high stability over large-area scanning tests. Employing sharp GaN NWs in active AFM cantilevers demonstrated improvement in the image resolution compared to the standard Si-tips and accomplished ~10 nm linewidth structures under applied bias in field emission lithography.

Degree Name

Optical Science and Engineering

Level of Degree


Department Name

Optical Science and Engineering

First Committee Member (Chair)

Dr. Tito Busani

Second Committee Member

Dr. Steven R.J. Brueck

Third Committee Member

Dr. Daniel Feezell

Fourth Committee Member

Dr. Li Shi

Fifth Committee Member

Dr. Alejandro Manjavacas


Nanometrology, GaN Nanowires, Scanning Probe Microscopy, Nanoscale lithography, Nanophotonics

Document Type