Semiconductor Materials - 06

Abstract

Strain engineering in 2D semiconductors, particularly transition metal dichalcogenides (TMDs), enables tuning of their physical and chemical properties such as bandgap modulation and enhanced catalytic activity. It is possible to introduce built-in strain into the TMD lattice by chemical vapor deposition (CVD) growth, due to the thermal expansion coefficients mismatch between TMDs and substrates [1]. However, substrate surface imperfections including roughness and charged impurities often degrade the strain uniformity, limiting the potential of the strained TMDs. Here, we demonstrate the introduction of uniform tensile strain in monolayer TMDs directly grown on graphene/SiC substrates [2].

Graphene/SiC substrate was prepared by thermal decomposition of single-crystalline 4H-SiC(0001) substrate. Subsequently, monolayer WSe₂ and MoS₂ were grown via salt-assisted CVD. Cross-sectional scanning transmission electron microscopy (STEM) revealed the WSe₂/graphene/SiC heterostructure (Figure 1a). Orientation analysis indicates that WSe₂ grows via van der Waals epitaxy on the substrate. Photoluminescence (PL) spectrum of this sample exhibited a remarkably narrow linewidth of ~28 meV (Figure 1b), suggesting band modulation induced by tensile strain and suppression of inhomogeneous broadening. This uniform tensile strain is attributed to the small thermal expansion coefficient of SiC and the atomically-flat graphene surface. Furthermore, tensile-strained monolayer MoS₂ grown on graphene/SiC exhibited enhanced catalytic activity for the hydrogen evolution reaction. These findings highlight the versatility of the graphene/SiC substrate for the strain-engineered growth of 2D semiconductors.