Weng Junhui, Gao Shang-Peng
Department of Materials Science, Fudan University Shanghai 200433 P. R. China
RSC Adv. 2019 Oct 16;9(57):32984-32994. doi: 10.1039/c9ra06074j. eCollection 2019 Oct 15.
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.
随着微电子器件尺寸的减小，对超薄介电材料的结构稳定性和性质的理解变得越来越重要。通过计算研究了超薄ZrO（单层和双层）的结构和性质。生成焓和声子色散的计算表明，单层和双层ZrO采用类似于1T-MoS的蜂窝状结构时具有稳定性。此外，1T-ZrO单层或双层可以通过从非层状立方ZrO的(111)面解理来制备。而且，与立方ZrO中相应的平板相比，单层和双层ZrO中的面内晶格常数收缩与报道的实验观察结果一致。从GW方法计算得到的电子带隙表明，单层和双层ZrO都有较大的带隙，分别达到7.51和6.82 eV，这比ZrO所有体相的带隙都大。单层ZrO（ = 33.34， = 5.58）和双层ZrO（ = 33.86， = 8.93）的静态介电常数都大于单层h-BN（ = 6.82， = 3.29），并且可以观察到超薄ZrO中面外介电常数与层厚度之间有很强的相关性。因此，由于高介电常数、良好的热力学稳定性和大带隙，1T-ZrO在二维场效应晶体管和异质结应用中是一个有前途的候选材料。本文研究了ZrO-MoS异质结的界面性质和带边偏移，我们表明价带顶和导带底附近的电子态主要由单层MoS的贡献主导，并且与单层ZrO的界面将显著降低单层MoS的带隙。
