  Using first-principles calculations, we investigate six transition-metal
nitride halides (TMNHs): HfNBr, HfNCl, TiNBr, TiNCl, ZrNBr, and ZrNCl as
potential van der Waals (vdW) dielectrics for transition metal dichalcogenide
(TMD) channel transistors. We calculate the exfoliation energies and bulk
phonon energies and find that the six TMNHs are exfoliable and
thermodynamically stable. We calculate both the optical and static dielectric
constants in the in-plane and out-of-plane directions for both monolayer and
bulk TMNHs. In monolayers, the out-of-plane static dielectric constant ranges
from 5.04 (ZrNCl) to 6.03 (ZrNBr) whereas in-plane dielectric constants range
from 13.18 (HfNBr) to 74.52 (TiNCl). We show that the bandgap of TMNHs ranges
from 1.53 eV (TiNBr) to 3.36 eV (HfNCl) whereas the affinity ranges from 4.01
eV (HfNBr) to 5.60 eV (TiNCl). Finally, we estimate the dielectric leakage
current density of transistors with six TMNH monolayer dielectrics with five
monolayer channel TMDs (MoS2, MoSe2, MoTe2, WS2, and WSe2). For p-MOS TMD
channel transistors, 19 out of 30 combinations have a smaller leakage current
compared to monolayer hexagonal boron nitride (hBN), a well-known vdW
dielectric. The smallest monolayer leakage current of 2.14*10-9 A/cm2 is
predicted for a p-MOS WS2 transistor with HfNCl as a gate dielectric. HfNBr,
HfNCl, ZrNBr, and ZrNCl are also predicted to yield small leakage currents in
certain p-MOS TMD transistors.
