Modulation of Semiconductor Photoluminescence with Intense Terahertz Pulses

• Author / Creator

  Purschke, David N

• 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.

• Subjects / Keywords

  • Ultrafast
  • Terahertz
  • Luminescence

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3GF0N45R

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.