2D Metallic Transition Metal Dichalcogenides: Promising Contact Metals for 2D GaN-Based (Opto)electronic Devices

Abstract

Due to the high light absorption coefficient, excellent electronic mobility, and the enhanced excitonic effect, two-dimensional (2D) GaN materials hold great potential for applications in optoelectronic and electronic devices. As metal-semiconductor junction (MSJ) is a fundamental component of semiconductor-based devices, identifying suitable metal for contacting with semiconductor is essential. In this work, detailed first-principles calculations are performed to investigate the contact behavior between GaN monolayer (ML) and a series of 2D metals MX₂ (M = Nb, Ta, V, Mo, or W; X = S or Se). Despite the van der Waals (vdW) interface, Schottky barrier heights (SBHs) of MX₂/GaN MSJs are found significantly deviated from the Schottky–Mott limit. Stronger and weaker Fermi level pinning effects are identified in higher and lower work function (W_M) regions of metals, respectively. This is attributed to the asymmetric charge redistribution induced enhanced interface dipole (ΔP) in MSJs leading to the increased step potential (ΔV) as response of the increased W_M of MX₂. P-type quasi-Ohmic contact could be realized in Ga-top stacking H-TaS₂/GaN, H-NbS₂/GaN, and H-VS₂/GaN, indicating the potential application of 2D H-TaS₂, H-NbS₂, and H-VS₂ as electrode materials. Appling biaxial tensile strain is identified to be a feasible strategy for modulating the contact behavior in MX₂/GaN, as it could effectively tune the SBH, change the contact type, or induce Schottky to quasi-Ohmic contact transition. We demonstrate that strain effects on the contact properties of MX₂/GaN MSJs are both MX₂ and stacking configuration dependent, which are determined by the synergistic effect of strain-modulated ionization energy and electron affinity of GaN ML, W_M of MX₂, and ΔV- and ΔP-quantified interface coupling in MSJs. Our work not only offers insights for prospection into the fundamental contact properties of 2D metal/GaN vdW interfaces, but also provides electrode material selection and strain strategies to achieve Ohmic contact as well as tunable SBHs in 2D GaN, which helps give theoretical guidance for developing high-performance 2D GaN-based optoelectronic and electronic devices.