KPFM and CAFM based studies of MoS2 (2D)/WS2 heterojunction patterns fabricated using stencil mask lithography technique

Vertical heterojunctions formed by layer-by-layer stacking of two-dimensional (2D) transition metal dichalcogenides (TMDs) are believed to be the key element of next-generation optoelectronic devices. For developing devices based on such heterostructures, their patterned arrays at pre-defined locations are needed. Here, we present a novel route for achieving MoS2 (2D)/WS2 heterojunctions arrays by combining radio frequency (RF) magnetron sputtering, stencil mask lithography and vapour phase sulfurization. Kelvin probe force microscopy (KPFM) based surface potential measurements have been carried out to locate the Fermi level position in an individual MoS2 pattern and uncovered WS2 portion. For MoS2, Fermi level is found to be located at 4.6 eV which suggests its n-type nature while WS2 shows p-type nature with Fermi level lying just below the middle of the energy band gap. MoS2/WS2 heterojunctions are electrically characterized using conducting atomic force microscopy (CAFM) where localized I-V curves are obtained from a few random locations of these patterned heterojunctions. Rectifying I-V behaviour from each location confirms formation of the junctions with good point-to-point uniformity. Present study is an effort towards the fabrication of patterned arrays of vertical MoS2/WS2 heterojunctions and understanding the junction formation using KPFM and CAFM techniques.