  Strain engineering is an important method for tuning the properties of
semiconductors and has been used to improve the mobility of silicon transistors
for several decades. Recently, theoretical studies have predicted that strain
can also improve the mobility of two-dimensional (2D) semiconductors, e.g. by
reducing intervalley scattering or lowering effective masses. Here, we
experimentally show strain-enhanced electron mobility in monolayer MoS2
transistors with uniaxial tensile strain, on flexible substrates. The on-state
current and mobility are nearly doubled with tensile strain up to 0.7%, and
devices return to their initial state after release of strain. We also show a
gate-voltage-dependent gauge factor up to 200 for monolayer MoS2, which is
higher than previous values reported for sub-1 nm thin piezoresistive films.
These results demonstrate the importance of strain engineering 2D
semiconductors for performance enhancements in integrated circuits, or for
applications such as flexible strain sensors.
