Descriptor-Based Classification of Interfacial Electronic Coupling in Janus XP3-Based 2D Heterostructures

Abstract

Understanding and controlling interfacial electronic coupling in two-dimensional (2D) heterostructures is essential for designing functional materials for electronic, optoelectronic, and catalytic applications. Here, we investigate vertical heterobilayers constructed from two distinct XP3 monolayers (X = As, Ge, Sb, Bi, Sn, Al, Ga, and Pb) using first-principles density functional theory. The resulting Janus heterobilayers are energetically favorable and elastically stable, with electronic band gaps ranging from metallic and near-metallic to semiconducting regimes. Interlayer interactions induce significant band renormalization, including transitions between type I and type II alignment upon structural relaxation. To rationalize these effects, we establish a descriptor-based framework based on the metal metal interlayer distance, interfacial electron localization, and Bader charge redistribution. This combined analysis discriminates vdW-like, polar covalent, and ionic interaction regimes, with systematic trends governed by the average atomic number of the constituent elements. Optical absorption calculations indicate visible-to-near-infrared activity in selected systems, and band-edge alignment identifies promising candidates for selective redox processes. Overall, the proposed descriptor-based strategy provides a physically grounded route for identifying and engineering interfacial coupling in XP3 heterostructures and can be extended to other classes of two-dimensional material interfaces.

Figures (5)

• Figure 1: Top and side views of the optimized atomic structures of the investigated Janus XP$_3$ heterobilayers: (a) AlP$_3$/GaP$_3$, (b) AlP$_3$/PbP$_3$, (c) BiP$_3$/AlP$_3$, (d) BiP$_3$/GaP$_3$, (e) GaP$_3$/PbP$_3$, (f) GeP$_3$/SbP$_3$, (g) SbP$_3$/BiP$_3$, (h) SnP$_3$/AlP$_3$, (i) SnP$_3$/GaP$_3$, and (j) SnP$_3$/PbP$_3$. The dashed line represents the interlayer distance $\Delta h$, defined as the vertical separation between the metal atoms located at the centers of the two opposite layers forming the heterobilayer. The atomic species are identified by the following color code: light blue for Al, light green for Ga, dark gray for Pb, magenta for Bi, dark green for Ge, orange for Sb, purple for Sn, and light pink for P.
• Figure 2: Band edge alignment of the monolayers and heterostructures relative to the vacuum level (E - E$_{\rm{vac}}$). The yellow bars represent the conduction band minimum (E$_{\rm{CBM}}$), and the green bars correspond to the valence band maximum (E$_{\rm{VBM}}$). The horizontal colored regions indicate the redox potentials of water, with the upper band corresponding to the H$^{+}$/H$_{2}$ level and the lower band to the O$_{2}$/H$_{2}$O level. The color map represents the pH dependence of the redox potentials, varying continuously from pH 0 (blue) to pH 14 (red), as described by the Nernst equations \ref{['eq:1']} and \ref{['eq:2']}.
• Figure 3: Layer-projected electronic band structures of representative XP$_3$ heterostructures: (a) AlP$_3$/GaP$_3$, (b) AlP$_3$/PbP$_3$, (c) BiP$_3$/AlP$_3$, (d) BiP$_3$/GaP$_3$, (e) GaP$_3$/PbP$_3$, (f) GeP$_3$/SbP$_3$, (g) SbP$_3$/BiP$_3$, (h) SnP$_3$/AlP$_3$, (i) SnP$_3$/GaP$_3$, and (j) SnP$_3$/PbP$_3$. The dashed horizontal line indicates the Fermi level set to zero energy. The color scale represents the relative contribution of each constituent monolayer to the electronic states, allowing identification of band localization and interlayer hybridization near the valence and conduction band edges.
• Figure 4: (a) Electron localization function (ELF) mapped along the interlayer direction across the interface, illustrating the spatial evolution of electronic localization between the stacked XP$_3$ monolayers. (b) Scatter plot of ELF$_\mathrm{mid}$ as a function of the equilibrium interlayer distance $d_{\rm{X_AX_B}}$, where the marker size is proportional to the magnitude of the Bader charge transfer $|\Delta \rho|$, and the color scale represents the average atomic number $\bar{Z}$ of the constituent metal atoms.
• Figure 5: Absorption spectra of representative XP$_3$ heterostructures: (a) AlP$_3$/GaP$_3$, (b) AlP$_3$/PbP$_3$, (c) BiP$_3$/AlP$_3$, (d) SbP$_3$/BiP$_3$, and (e) SnP$_3$/AlP$_3$. Solid curves correspond to spectra calculated within the Bethe–Salpeter Equation (BSE) formalism, while dashed curves represent the Independent Particle Approximation (IPA). Red and purple lines denote light polarized along the $xx$ and $yy$ directions.