Insight into the stacking and the species-ordering dependences of interlayer bonding in SiC/GeC polar heterostructures

Abstract

Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce the π-π orbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si-C and C-Ge species orderings but weak hybridization in the case of the C-C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si-C and C-Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C-C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si-C ordering (or under the AB stacking with C-C ordering). While a direct band gap of 2.00 eV – 2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.

Crucial role of interfacial interaction in 2D polar SiGe/GeC heterostructures

“…−27.08 meV atom −1 in bilayer graphene [47] and −20.75 meV atom −1 in graphene/h-BN-VH [28]) and comparable to other heterostructures stacked by 2D polar materials (e.g. ∼−41.55 meV atom −1 in SiC/GeC-VHs [48], ∼−48 meV atom −1 in AlAs/germanene-VH [29], and ∼−48.9/54.5 meV atom −1 in SiC(GeC)/MoS 2 -VHs [49]). This interesting finding implies that the existence of the electrostatic interlayer interaction in hybrid 2D polar-VHs, together with the vdW interaction, plays a key role in stabilizing the combined 2D polar bilayers.…”

“…the feature of semimetal/semiconductor heterojunction), like the Graphene/h-BN heterostructure [60]. Considering the calculated bandgaps of the pristine SiGe (∼0.32 eV at the HSE06 level) and GeC (∼2.84 eV at the HSE06 level [48]) monolayers, it is expected that commensurate SiGe/GeC-VHs, different from type-II heterojunctions, possess a wide spectrum of light absorption capabilities, spanning from ultraviolet to near infrared. The built-in electric field (E in ) in the interfacial region, on the other hand, plays a key role in carrier migration and enhance the efficiency of light-matter interactions.…”

Two-dimensional heterostructures formed by graphenelike ZnO and MgO monolayers for optoelectronic applications

“…The fascinating properties of mentioned pionering structures have inspired researchers to probe other novel vdWHs, and several structures have been already explored [38][39][40][41][42][43][44][45][46][47]. The most straightforward possible structures within this category are those formed by different binary monolayers.…”