Event
Ph.D. Research Proposal: Atiqur Rahman
Thursday, February 26, 2026
2:00 p.m.
IREAP Large Conference Room (ERF 1207)
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Atiqur Rahman
Committee:
Professor NAME (Chair): Thomas E. Murphy
Professor NAME: Yanne K. Chembo
Professor NAME: Carlos A. Ríos Ocampo
Date/time: February 26, 2026 / 2.00-4.00 PM
Location: IREAP Large Conference Room (ERF 1207)
Title: Electro-Optic Characterization of Monocrystalline and Polycrystalline Aluminum Nitride
Abstract: The crystallinity of a material often affects its material properties. In recent decades, aluminum nitride (AlN) has become a promising material for photonics. Depending on the substrate and growth technique, AlN can be either monocrystalline or polycrystalline. Polycrystalline AlN shows in-plane grain boundaries but the columnar cluster structures are mainly along the c-axis. In addition, the size of the coarse grain causes large surface roughness. Due to boundary scattering and defect absorption, polycrystalline AlN experiences optical losses. As there are no grain boundaries in monocrystalline AlN, the surface is smoother and it offers less boundary scattering loss and defect related absorption.
The electro-optic (EO) coefficients of bulk monocrystalline and polycrystalline AlN have been reported previously. Nevertheless, to the best of our knowledge, the EO coefficient of thin-film monocrystalline AlN is yet to be reported. Here we propose and demonstrate a method to measure the EO coefficient of thin-film monocrystalline AlN and compare side by side with the EO coefficient of polycrystalline AlN. We measured the EO coefficients for both transverse electric (TE) and transverse magnetic (TM) modes in the telecom C-band using the resonant shift of a microring resonator. We find surface effects that lead to bias drift for monocrystalline AlN, which can be eliminated by post-fabrication annealing. Also, we find screening effect for polycrystalline AlN which we eliminate by grounding the substrate or removing the bottom substrate. We found that the EO coefficients for monocrystalline and polycrystalline AlN are of similar order, with annealed monocrystalline AlN having a somewhat higher EO coefficients.
