Electronic and optical properties of InN-MTe₂(M=Mo, W) heterostructures from first-principles

Abstract

Heterostructures based on two-dimensional (2D) materials with tunable electronic and optical properties provide new chances for electronic and optoelectronic devices. Here we perform a comprehensive study on the electronic and optical properties of small-lattice-mismatched InN-MTe₂ (M = Mo, W) heterobilayers by first-principles based on density functional theory (DFT) with van der Waals corrections. The results demonstrate that the most stable stacking models of InN–MoTe₂ and InN–WTe₂ heterostructures are the same. Additionally, the band structures of InN-MTe₂ heterostructures are systematically explored with the consideration of spin-orbit coupling (SOC) effect. Analysis of the dielectric function and absorption coefficient of InN–MoTe₂/WTe₂ heterostructures show the enhanced response to UV and visible light compared to their individual InN, MoTe₂, and WTe₂ monolayers. In particular, electronic characteristics and structural stability can be modulated by changing the direction and intensity of an external electric field. The application of biaxial strain to InN–MoTe₂/WTe₂ not only able to tune the band gaps, but also change the light absorption performance. These findings provide new prospects for optoelectronic devices based on InN-MTe₂ heterostructures.

Introduction

Since the emergence of graphene [1], two-dimensional (2D) atomic layered systems have attracted tremendous interests due to their great promising applications on electronic and optoelectronic devices [[2], [3], [4], [5]]. Among of these 2D families, the group-VI elemental transition-metal dichalcogenides (TMDs) have been popularly used and investigated due to their superior physical properties and unique layered structures [[6], [7], [8]]. TMDs are part of the emerging 2D layered van der Waals (vdW) materials which could be stripped from bulk structures or obtained by chemical vapor deposition (CVD). Compared with the gapless graphene, experimental results exhibit that the band gaps of MoS₂, MoSe₂, and WS₂ monolayers range from 1.6 to 2.0 eV [9]. Additionally, Ruppert et al. successfully synthesized the single layer structure of MoTe₂ and further developed some new devices based on these TMDs. The optical gap of monolayer MoTe₂ is estimated to be about 1.1 eV by photoluminescence characterization, which is predicted as the narrowest band gap among the TMDs and is consistent with the theoretical calculations [10]. Meanwhile, it has been reported that indirect-direct band gap transitions could occur in TMDs heterobilayers with biaxial tensile strain or external electric fields, making TMDs heterobilayers materials a potential application for optical devices [11]. In addition, the spin–orbit coupling (SOC) effect is particularly obvious in the electronic structures of TMDs because of the combination of 4d or 5d transition-metal atoms and lack of inversion symmetry. Thus, the significant SOC of TMDs constitute an excellent research goal which reveals unique physical properties and extensive applications [12,13].

On the other hand, 2D III−V nitride semiconductors have attracted widespread interests due to their great chemical and thermal stability, and high thermal conductivity [14,15]. The successful acquisition of 2D GaN and AlN in experiments paved the way for optical and electronic nanodevices based on 2D nitrides [16,17]. Particularly, among the semiconductors of III-V nitride (AlN, GaN, InN) compounds, InN exhibits the smallest band gap in the infrared wavelength region, the highest absorption coefficient and carrier mobility, which deserves a promising candidate for optoelectronic applications [18,19]. However, due to the large substrate lattice mismatch, it is difficult to grow or synthesize InN in its bulk form, 2D InN appears to be the rarely studied materials among the III-V nitrides.

Considering a real application in electronic or optoelectronic devices, it is noted that the aforementioned materials individually has important ingredients for designing devices. More importantly, the lattice mismatch ratio between monolayer hexagonal InN and MTe₂ (M = Mo, W) is less than 1.5%, which might be beneficial for forming high-quality heterogeneous bilayers experimentally. As a result, it can be predicted that by combining the individual 2D materials into novel heterostructures, new interesting properties should be indeed worthy of exploration. Thus, we propose the heterostructures based on monolayer hexagonal InN and MTe₂ (M = Mo, W) to comprehensively investigate their electronic and optical properties by vdW-corrected density functional theory (DFT) calculations. The stacking mode, band structure, binding energy, projected density of states, and dielectric constant of InN-MTe₂ heterostructures are systematically calculated, while SOC effect is especially considered in the electronic properties of the heterostructures. More importanly, the band gaps, stability and adsorption coefficient of the InN-MTe₂ heterostructures could be effectively tuned by employing the external E-field and biaxial strain. These findings indicate that the InN-MTe₂ heterostructures could potentially serve as candidate materials for optoelectronic devices.