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4Gapped bilayer graphene for terahertz and infrared
photodetection
E. Titova12*, M. Kashchenko12, D. Mylnikov1, V. Semkin1, I. Domaratskiy1, D. Bandurin3, D. Svintsov1
1- Center for Photonics and 2D Materials, Moscow Institute ofPhysics and Technology, Dolgoprudny 141700, Russia 2- Programmable Functional Materials Lab, Center for Neurophysics and Neuromorphic Technologies, Moscow
127495, Russia
3- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
Terahertz (THz) and infrared (IR) detectors are used in many areas of science and technology -from wireless communication systems and medical scanning to the study of astronomical objects. However, in this range of electromagnetic radiation there is a dip in the sensitivity of photodetectors compared to detectors in the neighboring optical and radio ranges. Graphene has a number of unique properties that make it possible to use this material for effective terahertz detection [1]. For example, graphene exhibits low heat capacity and high phonon energy, which leads to rapid heating of photoinduced electrons and slow cooling of them on the crystal lattice. Due to the effect of "hot electrons" in graphene, the photo-thermoelectric effect is large, which can be used for photodetection in structures with a lateral p-n junction [2]. The use of bilayer graphene makes it possible to increase the temperature sensitivity of the material due to the possibility of electrostatically inducing a band gap in bilayer graphene, potentially resulting in a stronger photo-thermoelectric response.
In this work, we investigated graphene photodetectors, which are transistor structures based on bilayer graphene with lateral p-n junctions. We have shown that inducing a bandgap in bilayer graphene improves the terahertz responsivity and noise equivalent power (NEP) of the detector several times (see Fig. 1). The maximum responsivity at cryogenic temperature in our detectors reached 50.5 kV/W for voltage and 22.8 A/W for current, while the NEP dropped to 36.4 fW/Hz12 with band gap induction up to 25 meV [3]. The dominant rectification mechanism at cryogenic temperatures is photo-thermoelectric, against which there are features of an additional mechanism - presumably, rectification at tunnel junctions. We demonstrated the presence of tunnel transport in our structures based on photoresistivity analysis [4].
Figure 1. Schematic representation of the transistor structure based on bilayer graphene, as well as the dependence of THz responsivity and NEP on the band gap in the structure.
We also studied low-resistance edge states in the graphene channel, which manifest themselves in the saturation of the channel resistance as a function of the band gap in graphene. We have shown that using structures with a natural graphene edge, as opposed to a chemically etched edge, eliminates such edge states. We have shown that ON/OFF current ratios can exceed 105 in natural edge graphene transistors [5].
In addition, we studied similar graphene phototransistors at room temperature. We have shown that such transistors can serve as photodetectors in both the terahertz and infrared ranges.
[1] F. Bonaccorso, et al, Nature Photonics, Vol. 4, 2010.
[2] N.M. Gabor, et al, Science, Vol. 334, Issue 6056, 2011.
[3] E. Titova, et al, ACS Nano, 17, 9, 8223-8232, 2023.
[4] D. Mylnikov, et al, Nano Letters, 23, 1, 220-226, 2023.
[5] I.K. Domaratskiy, et al, Russian Microelectronics, Vol. 52, 2023.
