A new type-II lepidocrocite-type TiO2/GaSe heterostructure: Electronic and optical properties, bandgap engineering, interaction with ultrafast laser pulses

Abstract

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 planaraveraged 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.

Tuning the Electronic Properties of Two-Dimensional Lepidocrocite Titanium Dioxide-Based Heterojunctions

“…These values fall within the optimal range of vdW interaction, as discussed by Wang et al 49 and Pushkarev et al 50 The smaller interlayer distance in the TiO 2 /MoSSe may be attributed to a larger covalent radius of the Se atoms than the S atoms, resulting in a larger spacing between the monolayers. 51,52 Interlayer distances smaller than 3 Å have also been reported in previous investigations on TiO 2 -based heterostructures 28,29,53 and other vdW heterostructures as well. 54−56 To estimate the stability of the heterostructures, we calculated the formation energies using the equation…”

“…9,46 Applying the Hubbard correction, a band gap of 3.30 eV was obtained, which compares better with the experimental value of 3.8 eV 10 and the previously obtained value using the GGA + U. 28 Previously, higher-level approximations were also applied to calculate the electronic structure. Using the HSE06 functional, Li et al 29 obtained a band gap of 3.87 eV, which is extremely close to the experimental value.…”

“…Our calculated lattice parameters are in agreement with existing research. 28,45 Furthermore, we calculated the electronic band structure of the monolayers (Figure S5). Using the GGA functional, we found a direct band gap of 2.76 eV at Γ for TiO 2 .…”

“…Previously, 2D lepidocrocite-type TiO 2 -based vdW heterostructures containing GaSe and MoS 2 have been investigated for enhancing the performance of the isolated TiO 2 monolayer. 28,29 However, to the best of our knowledge, a vdW heterostructure of 2D TiO 2 and 2D MoSSe has not yet been studied. These materials have fairly similar lattice parameters (a = 3.00 Å and b = 3.80 Å for 2D TiO 2 , 30 and a = b = 3.24 Å for 2D MoSSe 22 ), which is essential in creating small lattice-mismatch heterostructures.…”