  The thickness-dependent band structure of MoS2 implies that discontinuities
in energy bands exist at the interface of monolayer (1L) and multilayer (ML)
thin films. The characteristics of such heterojunctions are analyzed here using
current versus voltage measurements, scanning photocurrent microscopy, and
finite element simulations of charge carrier transport. Rectifying I-V curves
are consistently observed between contacts on opposite sides of 1L-ML
junctions, and a strong bias-dependent photocurrent is observed at the
junction. Finite element device simulations with varying carrier concentrations
and electron affinities show that a type II band alignment at single
layer/multi-layer junctions reproduces both the rectifying electrical
characteristics and the photocurrent response under bias. However, the
zero-bias junction photocurrent and its energy dependence are not explained by
conventional photovoltaic and photothermoelectric mechanisms, indicating the
contributions of hot carriers.
