  Two-dimensional heterostructure of WSe2/MoS2 atomic layers has unique
piezoelectric characteristics which depends on the number of atomic layer,
stacking type, and interlayer interaction size. The van der Waals
heterostructure of p- and n-type TMDC atomic layers with different work
functions forms a staggered gap alignment. The large band offset of conduction
band minimum and valence band maximum between p-type WSe2 and n-type MoS2
atomic layers leads to the large electric polarization and piezoelectricity.
The output voltages for a MoS2/WSe2 partial vertical heterostructure with a
size of 3.0 nm and 1.5 nm were 0.137 V and 0.183 V for 4% and 8% tensile
strains, respectively. The output voltage of AB-stacking MoS2/WSe2
heterostructure was larger than that of AA-stacking heterostructure for 4%
tensile strain due to the contribution of intrinsic piezoelectricity and the
symmetric condition in out-of-plane. The AB-stacking has a lower formation
energy and better structural stability compared to AA-stacking. The large
output voltage of nanoscale partial or full vertical heterostructure of 2D
WSe2/MoS2 atomic layers in addition to the increased output voltage through
series connection of multiple nanoscale piezoelectric devices will enable the
realization of nano electromechanical systems (NEMS) with TMDC heterostructure
atomic layers.
