  Valley degree of freedom in the 2D semiconductor is a promising platform for
the next generation optoelectronics. Electrons in different valleys can have
opposite Berry curvature, leading to the valley Hall effect (VHE). However, VHE
without the plasmonic structure's assistance has only been reported in
cryogenic temperature, limiting its practical application. Here, we report the
observation of VHE at room temperature in the MoS2/WSe2 heterostructures. We
also uncover that both the magnitude and the polarity of the VHE in the 2D
heterostructure is gate tunable. We attribute this to the opposite VHE
contribution from the electron and hole in different layers. These results
indicate the bipolar transport nature of our valleytronic transistor. Utilizing
this gate tunability, we demonstrate a bipolar valleytronic transistor. Our
results can be used to improve the ON/OFF ratio of the valleytronic transistor
and to realize more versatile valleytronics logic circuits.
