  Recently, van der Waals heterostructure has attracted interest both
theoretically and experimentally for their potential applications in
photoelectronic devices, photovoltaic devices, plasmonic devices and
photocatalysis. Inspired by this, we design a lepidocrocite-type TiO2/GaSe
heterostructure. Via first-principles simulations, we show that such a
heterostructure is a direct bandgap semiconductor with a strong and broad
optical absorption, ranging from visible light to UV region, exhibiting its
potential application in photoelectronic and photovoltaic devices. With the
planar-averaged electron density difference and Bader charge analysis, the
heterostructure shows a strong capacity of enhancing the charge redistribution
especially at the interface, prolonging the lifetime of excitons, and hence
improving photocatalytic performance. By applying biaxial strain and interlayer
coupling, the heterostructure exhibits a direct-indirect bandgap transition and
shows a potential for mechanical sensors due to the smooth and linear variation
of bandgaps. Furthermore, our result indicates that a lower interlayer distance
leads to a stronger charge redistribution. The calculation of irradiating
ultrafast on the heterostructure further reveals a semiconductor-metal
transition for the heterostructure. Moreover, we find an enhanced induced
plasmonic current in the heterostructure under both x-polarized and z-polarized
laser, which is beneficial to plasmonic devices designs. Our research provides
valuable insight in applying the lepidocrocite-type TiO2/GaSe heterostructure
in photoelectronic, photovoltaic, photocatalytic, mechanical sensing and
plasmonic realms.
