Abstract
We report efficient photoconductivity multiplication in few-layer 2H-MoTe2 as a direct consequence of an efficient steplike carrier multiplication with near unity quantum yield and high carrier mobility (∼45 cm2 V–1 s–1) in MoTe2. This photoconductivity multiplication is quantified using ultrafast, excitation-wavelength-dependent photoconductivity measurements employing contact-free terahertz spectroscopy. We discuss the possible origins of efficient carrier multiplication in MoTe2 to guide future theoretical investigations. The combination of photoconductivity multiplication and the advantageous bandgap renders MoTe2 as a promising candidate for efficient optoelectronic devices.
Highlights
Photoexcitation of semiconductors with photon energies exceeding their bandgap (Eg) creates energetic electrons and holes
Optical generation of multiple pairs of electrons and holes in semiconductors by an energetic photon, a process known as carrier multiplication (CM) or multiexciton generation (MEG),[2] provides a novel solution to circumvent the energy losses in hot carriers relevant for high-efficiency photovoltaics
Substantial previous research has aimed at quantifying the CM efficiency and obtaining a fundamental understanding of the CM mechanism with a primary focus on semiconducting quantum dots (QDs).[3−11] The benefits from strong quantum confinement for CM in QDs come from the enhanced Coulomb interaction and relaxed momentum conservation condition
Summary
Photoexcitation of semiconductors with photon energies (hυ) exceeding their bandgap (Eg) creates energetic electrons and holes. In most semiconductors, these so-called hot carriers can cool down to the band-edge via carrier-phonon scattering, on a subpicosecond time scale. These so-called hot carriers can cool down to the band-edge via carrier-phonon scattering, on a subpicosecond time scale Such ultrafast energy loss via hot carrier cooling accounts for over ∼30% efficiency reduction within the Shockley and Queisser framework.[1]. Previous theoretical[12,13] and experimental[14−17] studies have shown that the reduced density of states imposed by confinement may constrain the energy conservation condition so that quantum confinement does not necessarily facilitate
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