Electromechanical switching and momentum-selective transport in geometry-defined blue phosphorus homojunctions

Developing intrinsic homojunctions without chemical heterogeneity remains a key challenge for the development of future two-dimensional devices. Here, we report a geometry-defined metal–semiconductor–metal homojunction in bilayer blue phosphorus (BlueP) created by a localized bubble corrugation, without chemical doping or foreign-material interfaces. First-principles calculations show that enlarging the interlayer separation in the metallic A 1 B − 1-stacked BlueP bilayer opens a bandgap, enabling a semiconducting barrier embedded between metallic segments. First-principles quantum-transport simulations reveal a crossover from ballistic to tunneling transport upon bubble formation. In the tunneling regime, transmission decreases exponentially with bubble width while remaining weakly sensitive to bubble height and bulging direction. The junction acts as an orientation-dependent k-space filter, producing transport anisotropy and momentum selectivity. Orbital-resolved scattering analysis shows that intralayer-bonding channels persist under deformation, whereas interlayer-hybridized channels are quenched, and that σ-type bonding yields higher conductance than π-type bonding. These insights motivate two electromechanical device concepts: a mechanically switchable memory element with ON/OFF ratios up to 30 and a nanoscale sliding rheostat with reproducible exponential resistance tuning for Ångström-scale displacement sensing.