Field-induced electron–hole asymmetry and tunable thermoelectric transport in monolayer-bilayer phosphorene junctions

We investigate the quantum and thermoelectric transport in lateral monolayer–bilayer phosphorene junctions with armchair and zigzag interfaces. Using a tight-binding model combined with the Landauer–Büttiker formalism, we compute the conductance, Seebeck coefficient, power factor, and electronic figure of merit from the energy-dependent transmission function. The probability current density is also evaluated to characterize the spatial distribution of transport, allowing to resolve the dominant transport pathways across the interface. A perpendicular electric field applied to the entire system modifies the band structure in both regions of the phosphorene junctions in qualitatively different ways: in the monolayer region, it acts primarily as an electrostatic potential shift, whereas in the bilayer region, it breaks layer-inversion symmetry and reduces the band gap, which can be completely closed at a critical field strength. This contrasted response in the applied field induces a pronounced electron–hole asymmetry in the transmission and conductance, together with a field-driven redistribution of current between edge-dominated and bulk-dominated channels. As a consequence, the thermoelectric response near the Fermi energy is strongly enhanced and can be spectrally shifted by tuning both the magnitude and polarity of the electric field. Our results show that monolayer–bilayer phosphorene junctions constitute a useful model platform for investigating the electrostatic control of thermoelectric transport via band-structure engineering. These findings suggest that such systems may offer a promising route toward field-tunable nanoscale thermoelectric functionalities.