Abstract
We demonstrate emission of terahertz pulses from a BiVO4/Au thin film interface, illuminated with femtosecond laser pulses. Based on the experimental observations, we propose that the most likely cause of the THz emission is the Photo-Dember effect caused by the standing wave intensity distribution formed at the BiVO4/Au interfaces.
Highlights
Terahertz (THz) pulses can be generated in non-linear optical crystals, metals, and semiconductors using ultrashort laser pulses that excite currents and polarizations [1, 2]
In order to determine if the depletion field is responsible for the THz generation in our case, we included SiO2 dielectric layers of varying thickness between the BiVO4 layer and the gold layer
Due to the SiO2 layer, the carrier transport between gold and BiVO4 is strongly reduced, which should hinder the formation of a depletion field
Summary
Terahertz (THz) pulses can be generated in non-linear optical crystals, metals, and semiconductors using ultrashort laser pulses that excite currents and polarizations [1, 2]. Due to the depletion field present near the Schottky barrier, the photoexcited carriers accelerate and form a photocurrent normal to the surface which gives rise to THz emission [6,7,8,9]. When excited with femtosecond laser pulses, this gives rise to a laterally non-uniform carrier distribution, which emits THz radiation [15]. Samples with an insulating SiO2 layer in between the BiVO4 and the gold are found to emit THz signals comparable in strength to samples without such a layer This indicates that built-in electric fields, associated with Schottky barrier formation, are less likely to be the source of the emission. We propose the longitudinal photo-Dember effect as the generation mechanism responsible for the THz emission
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