Hydrogen passivation effects on band alignment in lateral 2D group-IV heterostructures: a first-principles study

We present a first-principles density functional theory (DFT) study of lateral two-dimensional (2D) heterostructures composed of group-IV monolayers (silicene and germanene) in both pristine and hydrogenated forms. We systematically investigate interfacial stability, band alignment, and Schottky barrier characteristics. Two different interface models are compared: (i) α-type, representing ideal junctions with abrupt covalent bonding, and (ii) β-type, characterized by atomic mixing. The effects of chemical composition, hydrogenation, and interface morphology on structural features such as buckling height and electronic band alignment are analyzed. Our results reveal that α-type interfaces are consistently more favorable than their β-type counterparts, exhibiting superior thermodynamic stability and reduced structural perturbation. Among the different heterostructures, fully hydrogenated SiH/GeH interfaces display the lowest formation energy, indicating excellent interfacial compatibility, while pristine Si/Ge interfaces exhibit the strongest cohesive bonding per atom, underscoring their exceptional thermodynamic robustness. In general, partial hydrogenation significantly increases the buckling asymmetry and electrostatic potential steps, leading to enhancement of band offsets. A Type-I band alignment is observed for the fully hydrogenated GeH/SiH heterostructure, resulting in carrier localization and enhanced electron–hole overlap. In contrast, semimetal–semiconductor junctions such as Si/SiH and Ge/SiH exhibit Schottky behavior with tunable barrier heights of up to 1.5 eV, indicative of strong rectification and suppressed carrier injection. The ohmic, rectifying, and charge-confining behaviors of the various junctions are analyzed in relation to their interfacial band alignments and Schottky barrier heights. These findings highlight the critical role of interface engineering in controlling the electronic properties of 2D lateral heterostructures for next-generation nanoelectronic applications.