Speaker: Alan C. Farrell
Affiliation: Ph.D. Candidate - UCLA
Abstract: Avalanche photodetectors (APDs) have become the technology of choice for the most demanding photon detection applications, including time-resolved photoluminescence, laser rangefinders, time-of-flight 3D scanners, and light detection and ranging (LiDAR). More recently, demand for high volume, low-cost LiDAR has seen a dramatic rise with the development and commercialization of autonomous vehicles. For many applications, silicon single photon avalanche diodes (SPADs) offer the best available performance in terms of dark count rate (DCR), photon detection efficiency (PDE), and timing jitter. However, in certain instances, e.g., quantum key distribution and eye-safe LiDAR, it is advantageous to be able to detect light in the near-IR, where silicon SPADs fail to offer acceptable PDE. Initially, standard commercially available InGaAs-InP separate absorption-multiplication (SAM) APDs were tested in Geiger mode, but the DCR of these detectors was very high. Later, InGaAs-InP SPADs specifically designed for single photon detection emerged that took into account the much higher electric fields present in the avalanche region of a SPAD to reduce trap-assisted tunneling responsible for the high DCR. Although considerable progress has been made towards improving performance—it is now common to achieve 10-20% PDE with a DCR of only a few kHz—there still exists a fundamental limit to the maximum count rate stemming from the need to incorporate a dead time in order to suppress afterpulsing.
The work presented here attempts to take advantage of the nanowire platform in order to reduce the DCR and eliminate afterpulsing effects. An InGaAs-GaAs nanowire SPAD can reduce the fill factor of a detector by two orders of magnitude while keeping the effective active area unchanged, reducing the DCR to 10’s of Hz or less. In addition, by confining each avalanche pulse to a single nanowire, the total volume exposed to the large current flow is negligible compared to a standard bulk SPAD. As a result, the total number of traps that are filled and then released is also negligible and afterpulsing effects are nearly eliminated. This allows the nanowire SPAD to operate in free-running mode, i.e., no dead time is used, and photon count rates up to 8 MHz are measured. Limitations of the current design and future prospects will also be discussed.
Biography: Alan Farrell received his B.S. in Physics in 2006 and M.S. in Astrophysics in 2010 from the University of Texas at Brownsville. He began his Ph.D. studies at UCLA electrical engineering in 2012, where he worked on the design and characterization of nanowire-based photodetectors. He was a recipient of the NSF Clean Green IGERT Fellowship, the Eugene V. Cota-Robles Fellowship, and the Dissertation Year Fellowship. Upon graduating from UCLA, he will join Northrop Grumman Corporation’s Future Technical Leaders (FTL) program.
Date(s) - Jun 05, 2017
4:00 pm - 6:00 pm
E-IV Tesla Room #53-125
420 Westwood Plaza - 5th Flr., Los Angeles CA 90095