Top electrode engineering for enhanced photoresponse in vertical graphene/Si photodetectors via Au grid electrode

Vertical graphene/Si heterojunction photodetectors are promising for broadband photodetection, yet their performance remains strongly constrained by the optical and electrical roles of the top electrode. Here, a vertical graphene/n-Si photodetector with a metal top electrode is systematically engineered to clarify how electrode structure and metal selection jointly govern optical coupling, carrier extraction, and overall photoelectric conversion. By combining three-dimensional finite-difference time-domain optical simulations with Silvaco TCAD electrical simulations, the optical absorption, carrier generation and photoresponse of the device are comparatively evaluated for continuous Au film and Au grid electrodes and two different top-electrode materials including Au and Pt. The results show that the optimized Au grid electrode effectively significantly improves optical transmittance while maintaining effective electrical continuity, thereby reducing shading losses and enhancing light coupling into the VG/Si heterojunction. Simulated spatial distribution of photogenerated carriers further confirms that the Au grid structure enables more efficient light delivery to the active region. The optimized device exhibits a peak photogenerated current of approximately 9.4 × 10 −7 A over the 700 nm∼1000 nm wavelength range and achieves a maximum responsivity of 3.6 A/W at a reverse bias of 1 V at 1550 nm. These findings demonstrate that the top electrode in vertical heterojunction photodetectors should be engineered as a coupled optical-electrical functional layer more than treated solely as a contact, and establish metal-electrode structure/material co-optimization as an effective route toward higher-performance graphene/Si vertical photodetectors.