Ph.D. Dissertation Defense: Lisa Krayer
Friday, November 15, 2019
10:00 a.m.-12:00 p.m.
301 405 3681
Professor Jeremy N. Munday, Chair/Advisor
Professor Neil Goldsman
Professor Thomas E. Murphy
Professor Lourdes G. Salamanca-Riba, Dean's Representative
Date/Time: Friday, November 15th, 2019 at 10 AM - 12 PM
Place: AVW 2460
Title: Photodetection using ultrathin metal films
scalable, lithography-free, and low-cost silicon-based optoelectronics beyond the material bandgap.
Light absorption in metal films can excite hot carriers, which are useful for photodetection, solar energy conversion, and many other applications. However, metals are highly reflective, and therefore, careful optical design is required to achieve high absorption in these films. Through appropriate optical design, we achieved a Fabry-P erot-like resonance in ultrathin metal films deposited on a semiconductor enabling > 70% light absorption below the bandgap of the semiconductor. We experimentally demonstrate this phenomenon with four ultrathin planar metal films: Pt, Fe, Cr, and Ti. These metals were chosen to satisfy the resonant condition for high absorption over a wide range of wavelengths, and with these designs we realize a near-infrared imaging detector.
Finally, we explore the possibility of tuning material properties through alloying metals. We explore AgAu alloys for controlling the optical and electrical responses to achieve improved functionality as hot carrier photodetectors. An ideal metal-semiconductor photodetector requires not only high absorption, but also long hot carrier attenuation lengths in order to efficiently collect excited carriers. While pure Ag and Au do not have high absorption, they have long hot carrier attenuation lengths >20 nm. We find that alloying Ag and Au enhances the absorption by ~ 50% while maintaining attenuation lengths >15 nm, although pure Au remains the best material for maximizing the hot carrier attenuation length because the alloys are limited by high grain boundary scattering.