Stacking-order-governed transport and hysteresis in BP–graphene heterojunctions

Two-dimensional (2D) van der Waals heterostructures enable flexible band engineering and interface design but remain highly sensitive to stacking sequence and interface quality. In this study, we systematically investigate the impact of stacking order on the electrical transport, gate-control behavior, hysteresis dynamics, and photo-response of BP/Gr (BP/Gr) and Gr/BP (Gr/BP) vertical heterojunction devices. The devices were fabricated via PDMS-assisted exfoliation and deterministic dry transfer, followed by electrode integration on Si/SiO₂ substrates. Structural imperfections arising from mechanical exfoliation, interfacial adhesion variability, and BP surface degradation were analyzed to assess their influence on device performance. Electrical measurements show that the absolute current magnitude is primarily determined by the effective BP–graphene contact area, while gate-modulation capability is controlled by the stacking order rather than contact geometry. Under reverse bias, the BP/Gr configuration exhibits strong gate sensitivity due to direct modulation of BP band bending and efficient reduction of the interfacial Schottky barrier, whereas the Gr/BP configuration demonstrates minimal gate-induced variation owing to electrostatic screening by the top-layer graphene. Transfer characteristics reveal distinct hysteresis behaviors between the two stacking configurations. Gr/BP devices display a steeper and narrower hysteresis loop, consistent with enhanced charge-trap responsiveness enabled by the proximity of graphene to the gate dielectric. This observation aligns with reported mechanisms involving interface traps, slow charge transfer, band bending, and interface polarization in 2D systems. Under 980 nm illumination, the photocurrent is found to be independent of gate voltage but strongly dependent on stacking order. BP/Gr devices generate photocurrent two orders of magnitude larger than Gr/BP due to the top-layer BP directly absorbing incident light, whereas the graphene-overlayer configuration partially blocks or attenuates illumination. Overall, the results demonstrate that stacking sequence plays a decisive role in determining interfacial electrostatics, barrier modulation, trap-state dynamics, and optical absorption pathways in BP–graphene heterojunctions. This work provides mechanistic insights and design guidelines for high-performance 2D optoelectronic devices and vertically stacked transistor architectures.