03/14/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Electrical and Computer Engineering, invites you to attend a doctoral dissertation defense by Ainaz Ghafary Aghdam on "Double-Pointed Optical Antenna and Shortwave Infrared Avalanche Photodiode."

Candidate Name: Ainaz Ghafary Aghdam
Degree: Doctoral
Defense Date: March 28, 2024
Time: 2 p.m. (ET)
Location: Zoom (email advisor to request the link)

Committee: 

  • Advisor: Joel Therrien
  • Jay A. Weitzen Department Chair, Professor, Ph.D., ECE Department, UMass Lowell
  • Jean-Francois Millithaler, Ph.D., Assistant Teaching Professor, ECE Department, UMass Lowell
  • Viktor A Podolskiy Assistant Chair, Graduate Coordinator, Ph.D., Professor, Physics Department, UMass Lowell

Brief Abstract:
The importance of infrared radiation in human life made it very attractive field that the research is ongoing in this area. Even though more than two centuries have passed since its discovery. During these years, the infrared detection has been received lots of attention and main research has been conducted to enhance the infrared photodetection performance. Surface Plasmonic Resonance is one of the methods that could enhance the performance of the photodetector.
Numerous attempts have been made in Center for Photonics, Electromagnetics and Nanoelectronics (CPEN) in University of Massachusetts Lowell to enhance the performance of photodetector made from different semiconductor materials in terms of QDIPs and PIN photodetectors. Different plasmonic structure like hole array, metallic disk array, metallic ring, pointed antenna has been fully investigated and the effect of parameters like diameter, length, period and metal thickness has been fully studied.

In this research, I want to present a new kind of plasmonic structure called Double-pointed optical antenna and its enhancement in the longwave infrared (8-12 um) spectral regime. This complex structure has sharp corners that can enhance the E-field. The Double-pointed Optical antennas have been simulated and compared with the Single-pointed Optical antenna. It is discovered that the Double-pointed Optical antennas show higher E-fields in the LWIR spectral regime for both the single antenna and coupled antenna configurations. I investigate how different geometry parameters such as the gap size, the length and the width affect the E-fields enhancement of the Double-pointed antenna. The uncoupled Double-pointed optical antenna can be modeled as an RLC circuit, whereas the coupled Double-pointed dipole antennas show clear Fano-type interference between the transmission and the discrete plasmonic resonant modes. The E-fields of the Double-pointed antenna are also compared to those of the bow-tie antennas with the same gap dimension.

Moreover, I want to report a new type of Avalanche photodetector that is made from InGaAsSb/GaSb with a separation between the absorption layer and the multiplication layer called Separated Absorption Multiplication (SAM) in short Infrared wavelength up to 2 μm. The APD is using for detecting very low-level signal and in the case that the noise of the amplifier is high it is one of the best choices. In addition, the SAM APD shows low dark current and high gain. The characteristics of this SAM APD has been tested and multiplication gain has been measured.