Dae-Sin Kim joined Prof. Citrin’s research group in 2002. His research project is on the physics, simulation, and design of photoconductive sources of transient terahertz pulses. Such devices at minimum consist of a high-mobility, short carrier lifetime semiconductor upon which are deposited metalized electrodes that can be electrically biased relative to each other. When an ultrafast optical pulse whose photon energy exceeds the bandgap of the semiconductor is incident on the device, the transient current due to the photogenerated electrons and holes acts as a source term in Maxwell’s equations leading to the emission of a single- or few-cycle electromagnetic pulse spectrally extending from dc to a few terahertz. While the use of photoconductive sources of terahertz transients is the most widely used table-top generation technique, the approach has hitherto been limited to the nano or microwatt range, with very poor optical-to-terahertz conversion efficiencies. Together with Prof. S. E. Ralph of the School of Electrical and Computer Engineering at the Georgia Institute of Technology and Dr. D. Denison of the Signature Technologies Laboratory of the Georgia Tech Research Institute, in whose groups device fabrication and characterization are carried out, Dae-Sin is exploring novel device geometries that we predict will lead both to higher optical-to-terahertz conversion efficiencies, as well as to higher terahertz output powers, in the milliwatt range that is needed for many applications.
The simulations are based on a self-consistent spatially resolved, time-domain solution of the Maxwell and Boltzmann equations for the electromagnetic field and the electron and hole distribution functions. The electromagnetic field is included within the finite-difference time-domain method while the carrier transport is computed using the Monte Carlo method including all relevant scattering mechanisms and subsidiary valleys in the bandstructure. Dae-Sin developed the code from scratch. In addition, Dae-Sin is studying the effects of changing the geometry of the optical excitation spot as well as the incorporation of various metalized structures, including electrodes, lenses, and antennae.
Research Interests
- Terahertz photoconductor (Auston) switches
- Monte Carlo electronic device simulation
- Mesoscopic electron transport
- Broadband terahertz applications
Page Last Updated: 9 August 2005