First-principles investigation of Al2CO/h-XN (X = B, Al, Ga) heterostructures: Stability, electronic structure, and HER activity

Abstract

This work reports first-principles investigations of stability and surface properties of Al2CO/h-XN (X = B, Al, Ga) heterostructures. The investigated heterostructures Al2CO/h-BN, Al2CO/h-AlN and Al2CO/h-GaN are direct bandgap semi-conductors possessing narrow band gaps 0.48 eV, 0.95 eV and 0.68 eV respectively. The investigation of different stacking configurations of the structures revealed that AB stacking particularly in Al2CO/h-AlN, exhibits superior stability with higher work of adhesion and lower interfacial energy due to enhanced covalent interactions. The assessment of dynamic and thermal stabilities of the heterostructures was made through phonon dispersion calculations and molecular dynamics simulations which revealed the absence of imaginary phonon frequencies and stable energy fluctuations at 300 K, confirming their potential for experimental synthesis. The electronic structure exhibits direct, narrow band gap semiconducting behavior of the heterostructures with Al2CO/h-AlN displaying the highest band gap with dominant contribution of Al2CO monolayer's electronic states near the Fermi level. The analysis pointed out the donor role of Al, Ga, and B whereas O, N, and C acted as acceptors, demonstrating the presence of van der Waals interactions in Al2CO/h-BN and covalent bonding in Al2CO/h-AlN and Al2CO/h-GaN. The formation of the heterostructures caused Fermi level realignment and charge transfer which developed an internal electric field from Al2CO to h-BN, h-AlN, and h-GaN, to influence band edge positions and thus photocatalytic activity. Though Al2CO/h-AlN and Al2CO/h-GaN are capable of hydrogen evolution reaction (HER) but Al2CO/h-AlN demonstrated excellent HER activity owing to low Gibbs free energy (ΔG = −0.171 eV) at N site of heterostructure. The application of electric field caused notable modulation of the band gap, indicating prospects to promote photocatalytic activity via control over the charge carrier separation. The calculations of absorption spectra and dielectric function of the heterostructures exhibit consistency of absorption offsets with band gaps to indicate resourceful photocatalysis based on effective photogenerated charge carrier separation. The NEGF results revealed possibility of direct-tunneling based enhancement in transmission near Fermi level in Au– Al2CO/XN-Au nanodevices with predominant Schottky rectification pointing towards its potential for enhanced carrier transport which is key to boost the photoelectrocatalytic efficiency of the heterostructures.

Keywords: 2D materials; DFT, HER, Heterostructures, NEGF, Photocatalysis.