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Modulation of Semiconductor Photoluminescence with Intense Terahertz Pulses Open Access


Other title
Type of item
Degree grantor
University of Alberta
Author or creator
Purschke, David N
Supervisor and department
Hegmann, Frank (Physics)
Examining committee member and department
Sydora, Richard (Physics)
Maciejko, Joseph (Physics)
Rozmus, Wojciech (Physics)
Department of Physics

Date accepted
Graduation date
2016-06:Fall 2016
Master of Science
Degree level
Over the last 5 years, tilted pulse-front terahertz (THz) generation has opened the door to new studies of nonlinear dynamics in a variety of materials. With access to strong electric fields that turn on and off over picosecond timescales exciting new possibilities exist to control light-matter interaction. We have developed a new intense THz pulse source, with a peak electric field of 230 kV/cm for exploring nonlinear dynamics in semiconductors. Here, we study the effects of THz pulses on semiconductor photoluminescence (PL). When a femtosecond optical and single-cycle intense THz pulse are simultaneously incident on a direct-gap semiconductor, the THz pulse enhances high energy and quenches low energy PL. However, with time delays larger than 1 ps, no modulation of the PL occurs. We have systematically studied the THz-pulse-induced change in PL (THz- _PL) over a wide range of THz energies and photoexcitation densities in gallium arsenide (GaAs) and indium phosphide (InP) to help understand the mechanism. In most cases, the quenching dominates and there is integrated PL quenching (PLQ). With increasing photoexcited carrier density, the fractional quenching decreases, while the enhancement increases, and less integrated modulation occurs. At high excitation density, by changing the temporal profile of the photoexcitation pulse, the enhancement can be made to dominate and there is integrated PL enhancement (PLE). The origin of this behaviour has to do with the redistribution of carriers in phase space by the strong electric field of the THz pulse. In real space, oppositely charged electrons and holes are spatially separated. In momentum space, hot electrons scatter to satellite valleys, increasing the rise-time of the PL, slowing carrier diffusion, and releasing a large number of high-wavevector phonons. Despite our understanding of these processes, a precise description of the THz-ΔPL is still not completely clear. Possible explanations for these effects are discussed, including suppression of stimulated emission, enhanced surface recombination, and non-radiative recombination involving intervalley phonons.
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