Electrical Transport Properties of Polymorphic MoS₂

The engineering of polymorphs in two-dimensional layered materials has recently attracted significant interest. Although the semiconducting (2H) and metallic (1T) phases are known to be stable in thin-film MoTe2, semiconducting 2H-MoS2is locally converted into metallic 1T-MoS2through chemical lithiation. In this paper, we describe the observation of the 2H, 1T, and 1T′ phases coexisting in Li-treated MoS2, which result in unusual transport phenomena. Although multiphase MoS2shows no transistor-gating response, the channel resistance decreases in proportion to the temperature, similar to the behavior of a typical semiconductor. Transmission electron microscopy images clearly show that the 1T and 1T′ phases are randomly distributed and intervened with 2H-MoS2, which is referred to as the 1T and 1T′ puddling phenomenon. The resistance curve fits well with 2D-variable range-hopping transport behavior, where electrons hop over 1T domains that are bounded by semiconducting 2H phases. However, near 30 K, electrons hop over charge puddles. The large temperature coefficient of resistance (TCR) of multiphase MoS2, 2.0 × 10-2K-1at 300 K, allows for efficient IR detection at room temperature by means of the photothermal effect.