Physics & Astronomy Colloquium | Physics and Astronomy

Narrow-gap semiconductor structures for optoelectronic applications

Professor Michael B. Santos; Homer L. Dodge Department of Physics & Astronomy, University of Oklahoma

The band offsets in arsenide/antimonide materials have been exploited for the development of optoelectronic devices for many years. In this talk, I will discuss recent developments in two collaborative projects on photovoltaic devices that take new advantage of the band offsets in these materials.

First, we are exploring the interband cascade architecture for thermophotovoltaic applications [Sol. Energy Mater. Sol. Cells 238, 111636 (2022)]. Each stage of a multi-stage device is composed of an absorber, electron barrier, and hole barrier, all made from InAs/GaSb/AlSb multilayers. Because each absorber is thinner than the carrier diffusion length, photo-generated carriers are collected efficiently. The unipolar barriers accomplish rectification without resorting to conventional p-n junctions. The internal series resistance between stages can be negligible because transport is facilitated with a semi-metallic interface.

Second, we are employing a novel strategy to harness hot-carrier effects for increasing the efficiency of a solar cell [Nature Energy 5, 336 (2020)]. In an antimonide/arsenide structure, hot electrons are stored in the upper L and X valleys of the absorber layer. The transfer of electrons to the upper valleys is accomplished through intervalley scattering and the Gunn effect. Luminescence data reveal a stable hot-carrier population at a relatively low excitation power.

Short Bio: Michael Santos is a Professor of Physics and the Charles L. Blackburn Chair in Engineering Physics at the University of Oklahoma, where he has worked since 1993. His research focuses on the growth of III-V semiconductors by molecular beam epitaxy and the application of these materials as sensors, optoelectronic devices, and platforms for studying quantum effects. His research has been supported by the NSF, DoD, DOE, and the semiconductor industry. He has been a visiting professor at Tohoku University and NTT Basic Research Laboratories in Japan. He was a postdoctoral researcher at AT&T Bell Laboratories, received a Ph.D. from Princeton University, and received a B.S. degree from Cornell University. In 2012, Prof. Santos was elected as a Fellow of the American Physical Society for growth of compound semiconductor nanostructures and spin transport. He has co-authored more than 250 papers on experimental semiconductor research.