Undergraduate Thesis Or Project
 

Time resolved terahertz spectroscopy of photocarrier dynamics in WSe2

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https://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/db78tm53t

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  • Semiconductors serve an integral role in our technologies today. However, with new advancements in ultra-fast electronics, we are approaching the fundamental speed limits of traditional silicon-based semiconductors. Silicon-based semiconductors typically exhibit photocarrier dynamics in nanosecond timescales. Transition metal dichalcogenides (TMDs) are 2D materials shown to exhibit photocarrier dynamics in picosecond time scales, far faster than silicon-based semiconductors. We performed terahertz time domain spectroscopy (THz-TDS) on a WSe2 sample to observe these excitation/relaxation dynamics. The sample was first excited by an optical pump pulse and analyzed by a THz probe pulse. The probe pulse path goes through a delay stage which creates a temporal reference frame for the data. We found that when WSe2 is excited by the optical pump pulse, the THz response shows ultrafast excitation of photocarriers on a sub-picosecond time scale and the slow relaxation exceeding 400 picoseconds. The THz fields induce non-linear dynamics of the photocarriers, exhibiting a decrease in THz absorption as the applied field strength exceeds ~100 kV/cm. The results demonstrate that 2D TMD’s are promising for use in ultra-fast and nano scale devices.
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