Towards band structure and band offset engineering of monolayer Mo _{(1− x )} W _{( x )} S ₂ via Strain

Abstract

Semiconducting transition metal dichalcogenides (TMDs) demonstrate a wide range of optoelectronic properties due to their diverse elemental compositions, and are promising candidates for next-generation optoelectronics and energy harvesting devices. However, effective band offset engineering is required to implement practical structures with desirable functionalities. Here, we explore the pressure-induced band structure evolution of monolayer WS2 and Mo0.5W0.5S2 using hydrostatic compressive strain applied in a diamond anvil cell (DAC) apparatus and theoretical calculations, in order to study the modulation of band structure and explore the possibility of band alignment engineering through different compositions. Higher W composition in Mo(1−x)W(x)S2 contributes to a greater pressure-sensitivity of direct band gap opening, with a maximum value of 54 meV GPa−1 in WS2. Interestingly, while the conduction band minima (CBMs) remains largely unchanged after the rapid gap increase, valence band maxima (VBMs) significantly rise above the initial values. It is suggested that the pressure- and composition-engineering could introduce a wide variety of band alignments including type I, type II, and type III heterojunctions, and allow to construct precise structures with desirable functionalities. No structural transition is observed during the pressure experiments, implying the pressure could provide selective modulation of band offset.

Unusual Pressure‐Driven Phase Transformation and Band Renormalization in 2D vdW Hybrid Lead Halide Perovskites

“…Overall bandgap change is quite monotonic with pressure and changes at dE gap / dP ≈ −35 meV GPa ‐1 . This value is much similar to other 2D inorganic excitonic semiconductors such as MoS 2 , MoSe 2 , and WSe 2 which is around −5 to −50 meV GPa ‐1 . Similar changes can also be traced from micro‐absorption measurements in Figure 4b.…”

Thickness-Dependent Semiconductor-to-Metal Transition in Molybdenum Tungsten Disulfide Alloy under Hydrostatic Pressure

“…This result can be a good response to the variation of Mo (1– x ) W x S 2 over the entire pressure range. Similarly, Nayak et al 31 and Kim et al 34 found that the bandgaps of bulk MoS 2 , Mo 0.5 W 0.5 S 2 , as well as WS 2 decrease continuously, whereas those of the monolayer and bilayer increase initially and then monotonously decrease to zero at which the metallization occurs with increasing pressure in terms of experimental measurements and ab initio calculations. Interestingly, higher W composition in monolayer Mo (1– x ) W x S 2 contributes to a greater pressure-sensitivity of direct bandgap opening.…”

“…19−22,24,26,27 On the other hand, the electronic properties have also been changed under hydrostatic pressure. 21,22,24,27,31−34 Especially, the bandgap of bulk TMDs was found to be reduced consequently and to become metallic with increasing pressure, whereas the bandgap of the monolayer gradually increased in the small pressure range. 21,22,31,32 Importantly, the evolution of band structure combined modulation of composition and number of layers under hydrostatic pressure has gained an increased interest.…”

“…In particular, external pressure can also be used as an effective method to modulate the relevant physical and chemical properties of 2D materials, and some achievements have been obtained, for example, MoS 2 and WS 2 monolayer, bilayer, and the corresponding bulk counterparts can undergo a semiconductor-to-metal transition under the condition of pressure. 19−34 Under the condition of hydrostatic pressure, the compressive rate in the direction of out-of-plane was significantly higher than that of in-plane because of their unique layered structures due to the strong intralayer ionic-covalent bonds and the weak interlayer van der Waals (vdW) interactions. 19−22,24,26,27 On the other hand, the electronic properties have also been changed under hydrostatic pressure.…”

Progress in Contact, Doping and Mobility Engineering of MoS2: An Atomically Thin 2D Semiconductor

“…Analogous to the case of composition-dependent band-gap tuning in conventional III-V semiconductor alloys [400][401][402][403], the band-structure and band-gap engineering of composition-tuned monolayer MoS 2 -based alloys is extremely promising for enabling 2D optoelectronic applications with tailored properties. Moreover, composition-engineering can be combined with techniques such as "pressure-engineering" to enable a wide variety of band-alignments in these 2D alloys, as shown in the case of Mo 1-x W x S 2 monolayers by Kim et al [404]. MoS2 and WS2 or MoS2 and MoSe2, respectively [388][389][390][391][392][393][394].…”