Semiconducting 2D crystals are currently receiving significant attention dueto their great potential to be an ultra-thin body for efficient electrostaticmodulation which enables to overcome the limitations of silicon technology.Here we report that, as a key building block for 2D semiconductor devices,vertical p-n junctions are fabricated in ultrathin MoS2 by introducing AuCl3and benzyl viologen dopants. Unlike usual unipolar MoS2, the MoS2 p-n junctionsshow (i) ambipolar carrier transport, (ii) current rectification via modulationof potential barrier in films thicker than 8 nm, and (iii) reversed currentrectification via tunneling in films thinner than 8 nm. The ultimate thinnessof the vertical p-n homogeneous junctions in MoS2 is experimentally found to be3 nm, and the chemical doping depth is found to be 1.5 nm. The ultrathin MoS2p-n junctions present a significant potential of the 2D crystals for flexible,transparent, high-efficiency electronic and optoelectronic applications.
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