Enhancing the Photodetector with Graphene
[POSTECH research team improves the photodetector performance of graphene-silicon photodetector]
The photodetector embedded in digital cameras and mobile phones now go beyond image recognition and enable biometric recognition such as fingerprint authentication and face recognition. The photodetector – often called the ‘eye of the image sensor’ – recognizes the image of an object and requires more sophisticated and stable recognition capabilities. Recently, a POSTECH research team has demonstrated a simple method to improve the detectivity of photodetectors.
A research team led by Professor Byoung Hun Lee and Dr. Tae Jin Yoo of the Center for Semiconductor Technology Convergence (CSTC) of POSTECH’s Department of Electrical Engineering has succeeded in fabricating a highly efficient photodetector using a graphene/p-type silicon junction structure. In particular, the team verified that the detectability and dark current characteristics can be easily enhanced by simply pre-doping the graphene. In recognition of its significance, the research finding was published in Laser & Photonics Reviews on June 16, 2021.
A photodetector is a device that detects an optical signal and converts it into an electrical signal. The researchers focused on improving its performance to detect even the small signals by doping the graphene with polyethyleneimine (PEI) and modulating the Schottky barrier height from 0.42 eV to 0.68 eV in the photodetector.
When the Schottky barrier height is adjusted to 0.26eV as in this method, the dark current of the photodetector is reduced three times (from 980nA to 219pA) compared to the undoped device. The photodetectivity in the near-infrared (850nm) also improved by 529% compared to the undoped graphene/p-type silicon photodetector.
This newly developed graphene-silicon heterojunction photodetector can reduce the power consumption by reducing standby power with low dark current and can detect even very small signals. For this reason, it shows promise to be highly applicable to devices that require extreme precision such as digital cameras, image sensors, motion recognition sensors, and optical communication systems, which are already becoming smaller and faster.
This newly developed method will undergo a technology transfer to Sigma Photonics – a start-up company producing graphene photodetector – and a possible commercialization.
“Using a very easy chemical doping method, the dark current in the photodetector has been dramatically reduced,” explained Professor Byoung Hun Lee of POSTECH. “We anticipate it to become the new technology to help accelerate the commercialization of graphene photodetector and to apply them to various sectors such as autonomous vehicles, image sensors, and optical communication.”
This research was supported by the Global Frontier Program through the Global Frontier Hybrid Interface Materials, Creative Materials Discovery Program, and Nano Materials Technology Development Program and the Graphene Varistor-based Ternary Logic Device Development and Integration, and the Architecture Research, and Sigma Photonics (2018) Project of the Ministry of Science and ICT of Korea.