Bottom-contact architectures with common electrode materials such as
gold are crucial for the integration of 2D semiconductors into existing
device concepts. The high contact resistance to gold—especially for bottom
contacts—is, however, a general problem in 2D semiconductor thin-film
transistors. Pyrimidine-containing self-assembled monolayers on gold
electrodes are investigated for tuning the electrode work functions in order
to minimize that contact resistance. Their frequently ignored asymmetric and
bias-dependent nature is recorded by Kelvin probe force microscopy through
a direct mapping of the potential drop across the channel during device
operation. A reduction of the contact resistances exceeding two orders of
magnitude is achieved via a suitable self-assembled monolayer, which vastly
improves the overall device performance.