Identifying Contact Barrier Types in Few-Layer MoS2 Devices Using Correlative IV, LBIC, and Bias-Dependent KPFM

Electrical contacts between metals and two-dimensional (2D) semiconductors such as molybdenum disulfide (MoS2) critically govern device performance, yet their microscopic and spatially varying contributions are difficult to disentangle with a single technique. Here we present an integrated experimental framework that combines current-voltage (IV) characterization, laser beam induced current (LBIC) mapping, and bias-dependent Kelvin probe force microscopy (KPFM) to correlate macroscopic transport with spatially resolved photocurrent and bias-induced potential distributions in few-layer MoS2 two-terminal devices under ambient conditions. IV measurements quantify the total resistance, its polarity dependence and the illumination response. LBIC maps the local photocurrent response with micrometer spatial resolution, separating photocurrent contributions from contact-induced electric fields and from temperature gradients. KPFM, operated under an applied static bias rather than in the conventional work-function mode, provides nanoscale-resolved potential distributions that resolve the relative bias-induced voltage drops at the contacts and in the channel. We apply this framework to three few-layer devices spanning low-resistance, asymmetric and annealing-sensitive contact regimes, one exhibiting ohmic-like and two exhibiting diode-like contact behavior and show that the combined data support a qualitative distinction between low-barrier (Ohmic-like) and contact-limited transport with Schottky-like and tunnel-like contributions and resolve the asymmetry between the two contacts. Thermal annealing strongly reduces the total resistance of a bilayer device and redistributes the voltage drop, while contact-related voltage losses remain. This correlative, readily implementable approach provides a practical diagnostic for locating and classifying contact-limiting regions in 2D devices, for distinguishing polarity-dependent behavior and for evaluating and tracking contact-optimization strategies.