Bipolar Photoresponse in Graphene/GaN Heterostructure and its Secure Function in Free‐Space Optical Communication

Abstract The free‐space optical communication is regarded as a promising technique for next generation networks. However, all the data are exposed in free space with high risk of being attacked or eavesdropping by unauthorized parties. Here, a bipolar photodetector based on the graphene/GaN heterojunction is demonstrated. The polarity of the UV light photocurrent is opposite to that of the red light photocurrent, which results from the interface state filling effect and hot carrier injection into graphene, verified by Kelvin probe force microscope measurement results. Four stable photocurrent levels are demonstrated with only a single graphene/GaN heterojunction via the photocurrent polarity control, which is employed for a secure capability in conventional optical communication by setting visible and UV light as secret and key information, respectively. The technique provides a new strategy to design photodetectors for information encryption technology.