Low work function
materials are essential for efficient thermionic
energy converters (TECs), electronics, and electron emission devices.
Much effort has been put into finding thermally stable material combinations
that exhibit low work functions. Submonolayer coatings of alkali metals
have proven to significantly reduce the work function; however, a
work function less than 1 eV has not been reached. We report a record-low
work function of 0.70 eV by inducing a surface photovoltage (SPV)
in an n-type semiconductor with an alkali metal coating. Ultraviolet
photoelectron spectroscopy indicates a work function of 1.06 eV for
cesium/oxygen-activated GaAs consistent with density functional theory
model predictions. By illuminating with a 532 nm laser we induce an
additional shift down to 0.70 eV due to the SPV. Further, we apply
the SPV to the collector of an experimental TEC and demonstrate an
I
–
V
curve shift consistent with
the collector work function reduction. This method opens an avenue
toward efficient TECs and next-generation electron emission devices.
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