A method to improve graphene–silicon photodetector detectivity.

Photosensors in digital cameras and mobile phones now perform biometric recognition, such as fingerprints and faces, beyond simply recognizing images. Photodetectors, the “eyes of image sensors,” therefore require increasingly precise and stable detection. A simple method to improve their light detection has been developed.

Professor Byoung Hun Lee and Dr. Taejin Yoo at the Center for Semiconductor Technology Convergence in Electrical Engineering successfully fabricated an efficient graphene/p-type silicon junction photodetector. Notably, simply predoping graphene improves detectivity and dark-current characteristics. The findings were published on the 16th in Laser & Photonics Reviews.

Photodetectors convert optical signals into electrical signals. The team doped graphene with polyethyleneimine (PEI), adjusting the Schottky barrier height from 0.42 eV to 0.68 eV to improve detection of small signals. With this 0.26 eV adjustment, the source reports a threefold dark-current reduction, from 980 nA to 219 pA. Detectivity at near-infrared 850 nm improved by 529% compared with undoped graphene/p-type silicon detectors.

The heterojunction detector's low dark current reduces standby power and enables detection of very weak signals. It is therefore promising for increasingly compact, high-speed digital cameras, image sensors, motion sensors, optical communications, and other precision applications. The team plans technology transfer to graphene photosensor startup Sigma Photonics and commercialization.

Lee said, “We dramatically reduced photosensor dark current using a very simple chemical doping method. We expect this technology to accelerate graphene photosensor commercialization and support applications in autonomous vehicles, image sensors, optical communications, and other industries.”

Support came from the Global Frontier project on 3D integrated semiconductor materials and applications; the Creative Materials Discovery project on multilevel material design and applications; the Nanomaterials Core Technology Development program; the Ministry of Science and ICT project on graphene barristor-based ternary logic devices, integration processes, and architectures; and startup Sigma Photonics (2018).