Entangled bulk-interface piezotronic effect in polar heterojunction

Piezotronics is new-branch interface engineering for efficient electromechanical coupling of semiconductor heterojunctions, with broad applications in tactile sensing, human-machine communications and tunable electronics. The piezotronic modulation is usually dominated by intrinsic inversion-asymmetry piezoelectric polarization, while the piezoelectric polarization induced by ubiquitous and field-induced structural asymmetry remains largely overlooked. Motivated by the symmetry-governed spin-orbit physics, we here reveal an entangled interface-bulk piezotronic effect in polar metal-insulator-piezoelectric semiconductor tunneling heterojunctions. The interface and electric-field-induced bulk piezotronic effects coexist and jointly modulate quantum tunneling transport and capacitance property. Depending on the polar direction of heterojunction, two piezotronic effects regulate the tunneling current either cooperatively or competitively through barrier-height modulation. External pressure and bias voltage can optimize the cooperation and competition. In addition, device capacitance shows the opposite cooperation–competition relationship because it is governed by barrier-width modulation. Therefore, cooperative current modulation is accompanied by competitive capacitance modulation, and vice versa, indicating their entangled relationship. This work establishes capacitance as an effective probe of hidden bulk piezotronic effects and provides a framework for designing interface-engineered tunneling sensors and mechanically tunable semiconductor devices.