  Lateral-hetero structures of atomic layered materials alter the electronic
properties of pristine crystals and provide a possibility to produce useful
monolayer materials. We reveal that metal-semiconductor-metal lateral-hetero
junctions of $1H$-transition-metal dichalcogenides intrinsically possess
conducting channels of electrons with spin-valley locking, e.g., gate
electrode. We theoretically investigate the electronic structure and transport
properties of the lateral-hetero junctions and show that the hetero-structure
produces conducting channels through the $K$ and $K'$ valleys in the
semiconducting transition-metal dichalcogenide and restricts the spin of the
conducting electrons in each valley due to the valley dependent charge transfer
effect. Moreover, the theoretical investigation shows that the hetero-junction
of WSe$_2$ realizes a high transmission probability for valley-spin locked
electrons even in a long semiconducting region. The hetero-junction also
provides a useful electronic transport property, a step-like I-V
characteristic.
