Thermal annealing enhancing interface coupling in graphene/MoSe₂ photodetectors towards high responsivity

Van der Waals heterojunctions (vdWHs) present a promising platform for ultrathin optoelectronics, yet their performance is often limited by weak and non-uniform interlayer coupling. Here, we systematically explore the thermal annealing strategy for enhancing interface coupling and improving detection performance. Multiscale characterizations demonstrate that annealing effectively eliminates interfacial residues, reduces lattice strain, and decreases interlayer spacing. These structural optimizations enhance wavefunction overlap, promote interlayer charge transfer, and strengthen the built-in electric field, as evidenced by Raman spectroscopy, photoluminescence (PL), and Kelvin probe force microscopy (KPFM). Consequently, the optimally annealed device (500 °C) exhibits a remarkable increase in photocurrent (I_ph) from 3.9 × 10^-6 A to 2.0 × 10^-4 A, with responsivity (R) rising from 11 to 564 A/W. This improvement is accompanied by an external quantum efficiency (EQE) of 1.3 × 10⁵%, a detectivity (D*) of 3.6 × 10¹¹ Jones, and the response rise/fall time of 4.7 ms/3.6 ms at a bias of 1 V. Under zero-bias operation, the device maintains a self-powered photoresponse with an I_ph of 7.01 × 10^-8 A and R of 0.195 A/W. This work elucidates the underlying mechanism by which thermal annealing strengthens vdWH interfaces and provides a practical, scalable approach for achieving high-performance next-generation optoelectronic applications.