Ultrabroadband Terahertz Spectroscopy of Semiconductor Nanostructures

Ultrabroadband Terahertz Spectroscopy of Semiconductor Nanostructures

Dr. Hyunyong Choi

Lawrence Berkeley National Laboratory, Berkeley, CA

Abstract

The terahertz (THz) electromagnetic wave - frequency range broadly defined as 0.1 – 30 THz (1 mm – 15 µm wavelength) - is at the interface of modern electronics and photonics. This electromagnetic spectrum has been much less explored and has been called the “terahertz gap” due to the lack of efficient, room-temperature sources and detectors. Despite these difficulties, there has been recent explosion of interest in using THz pulse to address many questions in chemistry, physics, and material sciences. Perhaps the most important aspect of contemporary electronics is to understand the charge conduction process. Typical electrical characterization of nanostructures (1 nm = 10-9 m) by attaching metal wires becomes an extremely challenging work to study those structures. One of many attractive features of the THz spectroscopy is it provides a non-contact electrical probe, thus circumvents many constraints of conventional measurement techniques. In this talk, I will discuss how ultrashort THz pulse from femtosecond (1 fs = 10-15 s) solid-state laser sources can be generated and detected, and further used to investigate dynamical or localized conduction processes in semiconductor nanostructures, e.g. graphene, carbon nanotube, semiconductor nanowire, and heterostructure solar cells. By measuring both amplitude and phase of the multi-THz waves, one can directly access the conductivity information of the nanostructures with sub-cycle temporal resolution.

Biography of the speaker: Hyunyong Choi received the B.S. degree in electrical and electronic engineering from Yonsei University, Seoul, Korea, in 2002 and the M.S. and Ph.D. degrees in electrical engineering and computer science from the University of Michigan, Ann Arbor, in 2004 and 2007, respectively. For his Ph.D. thesis, he investigated ultrafast electronic transport dynamics in quantum cascade lasers. Since then, he has been a Postdoctoral Fellow in Materials Sciences Division at Lawrence Berkeley National Laboratory, where he has been working on the application of ultrabroadband terahertz spectroscopy to semiconductor nanostructures. Dr. Choi is a member of the American Physical Society, the Optical Society of America, and the IEEE.