Graphene/PbTe/n-Si Heterojunction Photodetector with Quasi-Type-Ι Band Alignment Enables a Broadband and Bias-Tunable Photoresponse.

High-performance broadband photodetectors traditionally based on III-V and II-VI semiconductors, despite their commercial success in the near- and mid-infrared regions, suffer from high fabrication cost, poor CMOS compatibility, and the need for cryogenic cooling, thus limiting their large-scale integration. Here, we demonstrate a virtual graphene/PbTe/Si heterojunction photodetector fabricated by magnetron sputtering, offering a scalable and cost-effective route to high-performance optoelectronic devices. The device exhibits a bias-tunable photoresponse governed by quantum tunneling at the PbTe/Si interface. At ±3 V biases, the photocurrent differs by nearly 2 orders of magnitude under low light intensities, whereas a symmetric response with less than 5% variation is observed at high light intensities. Exploiting this nonlinear response, we establish a dual-mode optical communication scheme, where plaintext is transmitted at high intensities and encrypted inverse codes are generated under low intensities. This built-in encoding functionality enables a simple yet effective strategy for secure optical communication without complex external circuits. Moreover, the CMOS-compatible fabrication process ensures seamless integration with existing silicon photonic platforms, highlighting the potential of this approach for future large-scale on-chip optical communication technologies.