Lanthanum Oxyhalide Monolayers: An Exceptional Dielectric Companion to 2-D Semiconductors

The 2-D-layered dielectrics offer a compelling route toward the design of next-generation ultimately compact nanoelectronics. Motivated by recent high-throughput computational prediction of LaO
${X}$
(
${X}$
= Br and Cl) as the exceptional 2-D dielectrics that significantly outperform HfO2 even in the monolyaer limit, we investigate the interface properties between LaO
${X}$
and the archetypal 2-D semiconductors of monolayer transition metal dichacolgenides (TMDCs)
${M}\text{S}_{{2}}$
(
${M}$
= Mo and W) using the first-principle density functional theory (DFT) simulations. Because of interfacial charge transfer and the presence of interface dipole potential, the conduction and valance band offsets (VBOs) cannot be simply determined using Anderson’s rule. DFT calculations at the HSE06 level reveal exceptionally large band offsets between 1.12 and 2.40 eV. Based on the Murphy–Good electron emission model, we show that LaO
${X}$
is an excellent companion dielectric to
${M}\text{S}_{{2}}$
for both NMOS and PMOS applications, with leakage currents much lower than
${10}^{-{2}}$
Acm
$^{-{2}}$
. The presence of an interfacial tunneling potential barrier at the van der Waals gap (vdWG) further provides an additional mechanism to suppress the leakage current. Our findings reveal the promising role of LaO
${X}$
toward high-performance 2-D semiconductor transistor technology.