  By means of numerical simulation, we study in this work the effects of
uniaxial strain on transport properties of strained graphene heterojunctions
and explore the possibility to achieve good performance of graphene transistors
using these hetero-channels. It is shown that a finite conduction-gap can open
in the strain junctions due to the strain-induced deformation of graphene
bandstructure. These hetero-channels are then demonstrated to improve
significantly the operation of graphene field-effect-transistors (FETs). In
particular, ON/OFF current ratio can reach a value of over 10$^5$. In graphene
normal FETs, transconductance, though reduced compared to the case of
unstrained devices, is still high while good saturation of current can be
obtained. This results in high voltage gain and high transition frequency of a
few hundreds of GHz for a gate length of 80 nm. In graphene tunneling FETs,
subthreshold swing lower than 30 mV/dec, strong non-linear effects such as gate
controllable negative differential conductance, and current rectification are
observed.
