Optical-pump terahertz-probe measurements of photocarrier multiplication in 2D bulk single-crystal 2H-MoTe2

Published

May 17, 2024

Author(s)

Steven W. Robey, Sergiy Krylyuk, Albert Davydov, Edwin J. Heilweil

Abstract

Overcoming the Schockley-Queisser limit in photovoltaic systems is an ongoing focus. Processes such as impact ionization that produce carrier multiplication in bulk materials are typically inefficient due to the requirements of energy and momentum conservation. Transition metal dichalcogenides, which are of interest for numerous reasons have, additionally, recently been shown to exhibit very efficient carrier multiplication in thin films of 2H-MoTe2 and 2H-WTe2 formed by chemical vapor deposition (CVD). The photoinduced carriers exhibit ultrafast (< 1 ps) dynamics, presumably limited by surface and defect recombination in the film, that will be hard to translate to increased photovoltaic efficiency. We used optical-pump terahertz-probe techniques to investigate photoinduced carriers in bulk single-crystal material to determine if we observe the much longer lifetimes expected for an indirect semiconductor and if the efficiency for carrier multiplication is impacted in single-crystal form. THz techniques provide the opportunity to determine the frequency dependent characteristics and dynamics of carriers in semiconducting materials, in a non-contact format. For the single-crystal material we find the same increase in photocarrier production per photon as in CVD films, for excitation over twice the band gap, but the lifetimes are increased by orders of magnitude. We also find evidence of some carrier localization in the THz frequency response that is attributed to the high density of defects and impurities in bulk MoTe2.

Citation

The Journal of Physical Chemistry C

Pub Type

Journals

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Keywords

terahertz, pump-probe, carrier dynamics, transition metal dichalcogenide, photovoltaic, carrier multipication

Citation

Robey, S. , Krylyuk, S. , Davydov, A. and Heilweil, E. (2024), Optical-pump terahertz-probe measurements of photocarrier multiplication in 2D bulk single-crystal 2H-MoTe2, The Journal of Physical Chemistry C, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=957095 (Accessed October 31, 2025)