Graphene photodetectors with ultra-broadband and high responsivity at room temperature

• Published in: Nature nanotechnology Vol. 9; no. 4; pp. 273 - 278
• Main Authors: Liu, Chang-Hua, Chang, You-Chia, Norris, Theodore B., Zhong, Zhaohui
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.04.2014; Nature Publishing Group
• Subjects: 147/135; 639/925/918/1052; 639/925/918/1054; Absorption; Channels; Computer engineering; Gates; Graphene; letter; Light absorption; Materials Science; Nanotechnology; Nanotechnology and Microengineering; Photodetectors; Quantum dots; Spectra; Spectroscopy; Temperature; Tunnels (transportation); Ann Arbor Michigan; United States > US; Michigan
• ISSN: 1748-3387; 1748-3395
• DOI: 10.1038/nnano.2014.31

The ability to detect light over a broad spectral range is central to several technological applications in imaging, sensing, spectroscopy and communication 1 , 2 . Graphene is a promising candidate material for ultra-broadband photodetectors, as its absorption spectrum covers the entire ultraviolet to far-infrared range 3 , 4 . However, the responsivity of graphene-based photodetectors has so far been limited to tens of mA W −1 (refs  5 , 6 , 7 , 8 , 9 , 10 ) due to the small optical absorption of a monolayer of carbon atoms. Integration of colloidal quantum dots in the light absorption layer can improve the responsivity of graphene photodetectors to ∼1 × 10 7  A W −1 (ref.  11 ), but the spectral range of photodetection is reduced because light absorption occurs in the quantum dots. Here, we report an ultra-broadband photodetector design based on a graphene double-layer heterostructure. The detector is a phototransistor consisting of a pair of stacked graphene monolayers (top layer, gate; bottom layer, channel) separated by a thin tunnel barrier. Under optical illumination, photoexcited hot carriers generated in the top layer tunnel into the bottom layer, leading to a charge build-up on the gate and a strong photogating effect on the channel conductance. The devices demonstrated room-temperature photodetection from the visible to the mid-infrared range, with mid-infrared responsivity higher than 1 A W −1 , as required by most applications 12 . These results address key challenges for broadband infrared detectors, and are promising for the development of graphene-based hot-carrier optoelectronic applications. A pair of stacked graphene layers separated by a tunnel barrier show sensitive photodetection capabilities.