Combinatorial Large-Area MoS₂/Anatase–TiO₂ Interface: A Pathway to Emergent Optical and Optoelectronic Functionalities

Abstract

The interface of transition-metal dichalcogenides (TMDCs) and high-<i>k</i> dielectric transition-metal oxides (TMOs) had triggered umpteen discourses because of the indubitable impact of TMOs in reducing the contact resistances and restraining the Fermi-level pinning for the metal-TMDC contacts. In the present work, we focus on the unresolved tumults of large-area TMDC/TMO interfaces, grown by adopting different techniques. Here, on a pulsed laser-deposited MoS₂ thin film, a layer of TiO₂ is grown by atomic layer deposition (ALD) and pulsed laser deposition (PLD). These two different techniques emanate the layer of TiO₂ with different crystallinities, thicknesses, and interfacial morphologies, subsequently influencing the electronic and optical properties of the interfaces. Contrasting the earlier reports of n-type doping at the exfoliated MoS₂/TiO₂ interfaces, the large-area MoS₂/anatase-TiO₂ films had realized a p-type doping of the underneath MoS₂, manifesting a boost in the extent of p-type doping with increasing thickness of TiO₂, as emerged from the X-ray photoelectron spectra. Density functional analysis of the MoS₂/anatase-TiO₂ interfaces, with pristine and interfacial defect configurations, could correlate the interdependence of doping and the terminating atomic surface of TiO₂ on MoS₂. The optical properties of the interface, encompassing photoluminescence, transient absorption and <i>z</i>-scan two-photon absorption, indicate the presence of defect-induced localized midgap levels in MoS₂/TiO₂ (PLD) and a relatively defect-free interface in MoS₂/TiO₂ (ALD), corroborating nicely with the corresponding theoretical analysis. From the investigation of optical properties, we indicate that the MoS₂/TiO₂ (PLD) interface may act as a promising saturable absorber, having a significant nonlinear response for the sub-band-gap excitations. Moreover, the MoS₂/TiO₂ (PLD) interface had exemplified better phototransport properties. A potential application of MoS₂/TiO₂ (PLD) is demonstrated by the fabrication of a p-type phototransistor with the ionic-gel top gate. This endeavor to analyze and perceive the MoS₂/TiO₂ interface establishes the prospectives of large-area interfaces in the field of optics and optoelectronics.