Tailoring Semiconductor Lateral Multijunctions for Giant Photoconductivity Enhancement

Semiconductor heterostructures have played a critical role as the enabler for new science and technology. The emergence of transition-metal dichalcogenides (TMDs) as atomically thin semiconductors has opened new frontiers in semiconductor heterostructures either by stacking different TMDs to form vertical heterojunctions or by stitching them laterally to form lateral heterojunctions via direct growth. In conventional semiconductor heterostructures, the design of multijunctions is critical to achieve carrier confinement. Analogously, successful synthesis of a monolayer WS₂/WS_2(1−x)Se_2x/WS₂ multijunction lateral heterostructure via direct growth by chemical vapor deposition is reported. The grown structures are characterized by Raman, photoluminescence, and annular dark-field scanning transmission electron microscopy to determine their lateral compositional profile. More importantly, using microwave impedance microscopy, it is demonstrated that the local photoconductivity in the alloy region can be tailored and enhanced by two orders of magnitude over pure WS₂. Finite element analysis confirms that this effect is due to the carrier diffusion and confinement into the alloy region. This work exemplifies the technological potential of atomically thin lateral heterostructures in optoelectronic applications.

The successful synthesis of a monolayer lateral heterostructure with multijunctions WS₂/WS_2(1−x)Se_2x/WS₂ (x ≈ 0.15) by chemical vapor deposition is reported. The grown structures are characterized by Raman and photoluminescence. Using light-assisted microwave impedance microscopy, the multijunctions demonstrate that the local photoconductivity in the alloy region can be tailored and enhanced by two orders of magnitude over pure WS₂.

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