Doctor of Philosophy (PhD)
Optoelectronics is the field of technology concerned with the study and application of electronic devices that source, detect and control light. Here we focus on the optical communications field which relies on optical fiber systems to carry signals to their destinations operating in the near-infrared range. To improve the performance of current optical fiber systems, one of the paths is to develop better near-infrared photodetectors.
The current group of materials used for near-infrared photodetection relies in the III-V semiconductor family. Although their spectral photosensitivity correlates well with the near-infrared, response time performance and electronic circuit integration remain limited for this class of material. Complementary metal-oxide-semiconductor-Si photonics technology can be coupled with metal interface to form a Schottky barrier extending the silicon detection range to near-infrared. Above-equilibrium “hot” carrier generation in metals is a promising route to convert photons into electrical charge for optoelectronics. However, metals which offer both hot-carrier generation in the near-infrared and sufficient carrier lifetimes remain elusive. The aim of this thesis is to contribute to the development of a novel class of materials for near-infrared optoelectronic applications.
Early progress in hot-carrier generation showed that one can tune optical and electronic properties of noble metals by alloying. The performance of these noble-metals alloys relied however on visible light application. Transition metals have a band structure much more favorable for hot-carrier generation in the near-infrared. However, due to the electron-electron scattering rates, oxidation states, and broad, weak or absence plasmon resonance, they have not gained attention in this field. Prior to this thesis, no noble-transition alloy for hot-carrier generation had been reported.
Here, it is shown that a noble-transition alloy, AuxPd1-x, outperforms its constituent metals concerning generation and lifetime of hot carriers when excited in the near infrared. We show that at optical fiber wavelengths (e.g., 1550 nm) Au50Pd50 provides a 20-fold increase in the number of ~0.8 eV hot holes, compared to Au, and a 3-fold increase in the carrier lifetime, compared to Pd. In addition, we show that to keep their properties, these alloys should not be exposed to high temperatures (450 oC) during fabrication steps or application.
Figueiredo Stofela, Sara Karoline, "Noble-Transition Alloy Absorbers for Near-Infrared Hot-Carrier Optoelectronics" (2020). LSU Doctoral Dissertations. 5140.
McPeak, Kevin M.