Role of metal contacts on the electric and thermoelectric response of hBN/WSe2 based transistors

Transition metal dichalcogenides represent an emergent platform for energy conversion solutions at the nanoscale. The thermoelectric performances of devices based on two-dimensional materials rely not only on the electric and thermal properties of the used materials but also on device engineering. In actual devices, hybridization effects at the semiconductor/metal interface strongly affect the local band structure with important consequences on charge injection and thermoelectric response. Here, we investigate the role of different metal contacts (Ag, Pd, Co, Ti) on the electric and thermoelectric properties of hexagonal boron nitride-supported few layers WSe2 transistors. In our devices, we reveal a metal contact-dependent Seebeck response with high values of the Seebeck coefficient (S), up to similar to 180 mu V=K, and power factors (PF = S-2 sigma) as high as 2.4 mu W/cm K-2 (Co), in agreement with the state-of-the-art. Metal electrodes for which weak interface hybridization is theoretically expected (Ag) show the lowest electrical conductivity and the highest Seebeck coefficient. On the opposite, for expected strong interface hybridization (Pd, Co, Ti), electrical conductivity increases and slightly reduced S values are measured. Our work unveils the importance of metal contacts engineering to optimize the thermoelectric performances of actual few layers transition metal dichalcogenides based transistors.