posted on 2021-08-05, 12:03authored byVan Tu Vu, Thi Thanh Huong Vu, Thanh Luan Phan, Won Tae Kang, Young Rae Kim, Minh Dao Tran, Huong Thi Thanh Nguyen, Young Hee Lee, Woo Jong Yu
van
der Waals heterostructures (vdWHs) of metallic (m-) and semiconducting
(s-) transition-metal dichalcogenides (TMDs) exhibit an ideal metal/semiconductor
(M/S) contact in a field-effect transistor. However, in the current
two-step chemical vapor deposition process, the synthesis of m-TMD
on pregrown s-TMD contaminates the van der Waals (vdW) interface and
hinders the doping of s-TMD. Here, NbSe2/Nb-doped-WSe2 metal-doped-semiconductor (M/d-S) vdWHs are created via a
one-step synthesis approach using a niobium molar ratio-controlled
solution-phase precursor. The one-step growth approach synthesizes
Nb-doped WSe2 with a controllable doping concentration
and metal/doped-semiconductor vdWHs. The hole carrier concentration
can be precisely controlled by controlling the Nb/(W + Nb) molar ratio
in the precursor solution from ∼3 × 1011/cm2 at Nb-0% to ∼1.38 × 1012/cm2 at Nb-60%; correspondingly, the contact resistance RC value decreases from 10 888.78 at Nb-0% to 70.60
kΩ.μm at Nb-60%. The Schottky barrier height measurement
in the Arrhenius plots of ln(Isat/T2) versus q/KBT demonstrated an ohmic contact in the
NbSe2/WxNb1–xSe2 vdWHs. Combining p-doping in WSe2 and M/d-S vdWHs, the mobility (27.24 cm2 V–1 s–1) and on/off ratio (2.2 ×
107) are increased 1238 and 4400 times, respectively, compared
to that using the Cr/pure-WSe2 contact (0.022 cm2 V–1 s–1 and 5 × 103, respectively). Together, the RC value using the NbSe2 contact shows 2.46 kΩ.μm,
which is ∼29 times lower than that of using a metal contact.
This method is expected to guide the synthesis of various M/d-S vdWHs
and applications in future high-performance integrated circuits.