Structures and characteristics of atomically thin ZrO2 from monolayer to bilayer and two-dimensional ZrO2–MoS2 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 ZrO2 (monolayer and bilayer) have been investigated by ab initio calculations. The calculation of enthalpies of formation and phonon dispersion demonstrates the stability of both monolayer and bilayer ZrO2 adopting a honeycomb-like structure similar to 1T-MoS2. Moreover, the 1T-ZrO2 monolayer or bilayer may be fabricated by the cleavage from the (111) facet of non-layered cubic ZrO2. Moreover, the contraction of in-plane lattice constants in monolayer and bilayer ZrO2 as compared to the corresponding slab in cubic ZrO2 is consistent with the reported experimental observation. The electronic band gaps calculated from the GW method show that both the monolayer and bilayer ZrO2 have large band gaps, reaching 7.51 and 6.82 eV, respectively, which are larger than those of all the bulk phases of ZrO2. The static dielectric constants of both monolayer ZrO2 (ϵ‖ = 33.34, ϵ⊥ = 5.58) and bilayer ZrO2 (ϵ‖ = 33.86, ϵ⊥ = 8.93) are larger than those of monolayer h-BN (ϵ‖ = 6.82, ϵ⊥ = 3.29) and a strong correlation between the out-of-plane dielectric constant and the layer thickness in ultrathin ZrO2 can be observed. Hence, 1T-ZrO2 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 ZrO2–MoS2 heterojunction are investigated herein, and we show that the electronic states near the VBM and CBM are dominated by the contributions from monolayer MoS2, and the interface with monolayer ZrO2 will significantly decrease the band gap of the monolayer MoS2.