Wavelength-Controlled Triple-Mode Photoconductance-Polarity-Switching Field Effect Transistor for Secure Time-Variable Encrypted Optical Communication

The controllable polarity switch between positive photoconductance (PPC) and negative photoconductance (NPC) in a photodetector is essential for the realization of versatile, innovative applications. Incorporating polarity-switching photoconductance with other response states, yet still posing challenges, allows for encoding multidimensional distinguishable optical information within a single device, which holds great potential for broadening application scope. Herein, three wavelength-controlled photoresponse modes are present in MoS2-based field effect transistor with lightly doped Si substrate by combining positive/negative photocurrent polarities with slow/fast response speeds. Specifically, a slow PPC response at 520 nm, along with fast bipolar infrared responses (NPC at 980 nm, PPC at 1310 nm), is integrated within a single MoS2 device. The opposite sub-bandgap infrared photoresponses are ascribed to the synergism of the bolometric effect and interfacial photogating, influenced by electrons photogenerated in Si. Based on the triple polarity-switching characteristic of the MoS2 device, the triple-channel real-time secure optical communication system with time-variable encryption algorithms is demonstrated, exponentially increasing the difficulty of brute-force cracking by synchronizing the time-variable key channel with two information channels. This work not only enhances the understanding of sub-bandgap photoresponse mechanisms in 2D material photodetectors but also offers promising avenues for the development of optoelectronics-assisted wireless communication technologies.