Structures and characteristics of atomically thin ZrO from monolayer to bilayer and two-dimensional ZrO-MoS heterojunction.

The understanding of the structural stability and properties of dielectric materials at the ultrathin level is becoming increasingly important as the size of microelectronic devices decreases. The structures and properties of ultrathin ZrO (monolayer and bilayer) have been investigated by calculations. The calculation of enthalpies of formation and phonon dispersion demonstrates the stability of both monolayer and bilayer ZrO adopting a honeycomb-like structure similar to 1T-MoS. Moreover, the 1T-ZrO monolayer or bilayer may be fabricated by the cleavage from the (111) facet of non-layered cubic ZrO. Moreover, the contraction of in-plane lattice constants in monolayer and bilayer ZrO as compared to the corresponding slab in cubic ZrO is consistent with the reported experimental observation. The electronic band gaps calculated from the GW method show that both the monolayer and bilayer ZrO have large band gaps, reaching 7.51 and 6.82 eV, respectively, which are larger than those of all the bulk phases of ZrO. The static dielectric constants of both monolayer ZrO ( = 33.34, = 5.58) and bilayer ZrO ( = 33.86, = 8.93) are larger than those of monolayer h-BN ( = 6.82, = 3.29) and a strong correlation between the out-of-plane dielectric constant and the layer thickness in ultrathin ZrO can be observed. Hence, 1T-ZrO is a promising candidate in 2D FETs and heterojunctions due to the high dielectric constant, good thermodynamic stability, and large band gap for applications. The interfacial properties and band edge offset of the ZrO-MoS heterojunction are investigated herein, and we show that the electronic states near the VBM and CBM are dominated by the contributions from monolayer MoS, and the interface with monolayer ZrO will significantly decrease the band gap of the monolayer MoS.