High performance bilayer-graphene terahertz detectors

Abstract

We report bilayer-graphene field effect transistors operating as THz broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity~1.2V/W (1.3 mA/W) and a noise equivalent power~2×10 -9 W/√Hz in the 0.29-0.38THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.Generation and detection of radiation across the far infrared or Terahertz (THz) region of the electromagnetic spectrum is promising for a large variety of strategic applications, 1 ranging from biomedical diagnostics 2 to process and quality control, 3 homeland security 1 and environmental monitoring. 4 Due to its non-ionizing nature, 1 THz radiation can penetrate many commonly used dielectrics, 1 otherwise opaque for visible and mid-infrared light, allowing detection of specific spectroscopic features 5 with a sub-millimeter diffractionlimited resolution. µV/W and operating in photovoltage mode at much higher frequencies (2.5 THz).Here we report THz detectors operating at RT in either photovoltage or photocurrent mode with a significant enhancement of sensitivity and lowered NEPs compared to the state of the art. This is achieved by using either large (1 µm) gate lengths, or buried gate geometries on a bilayer graphene (BLG) FET. We use BLG instead of single layer graphene (SLG) since the modulation of carrier density was proved to be more effective in the former case, 19 allowing a higher responsivity at THz frequencies.The devices are prepared as follows. Flakes are mechanically exfoliated from graphite 24 on an intrinsic Si substrate covered with 300nm SiO 2 . BLGs are selected and identified by a combination of optical microscopy 25 and Raman spectroscopy. 26,27 These are then used to fabricate two sets of FETs (samples A, B). In A, source (S) and drain (D) contacts are patterned by electron beam lithography (EBL) and metal evaporation (5nm Cr /80 nm Au). The S contact is connected to one lobe of a 50° bow-tie antenna, and D to a 3 metal pad. After placement of 35nm HfO 2 by atomic layer deposition (ALD), the other lobe of the antenna is fabricated, and constitutes the FET gate (g). The channel length is L SD = 2.5 m, while the gate length w G =1 m (Fig. 1a). In B, one lobe of a log-periodic circular-toothed antenna is fabricated by EBL and metal evaporation to act as buried gate. After deposition of 35 nm HfO 2 by ALD, S and D electrodes are fabricated.Similar to sample A, S is the second lobe of the antenna, while the drain is a metal line connecting to a bonding pad. The channel length is 2.5 m, its width 7.5 m, while w G = 0.3m (Fig. 1b). A BLG flake is then placed onto the pre-fabricated electrodes by wet transfer. 28 Fig. 2 compares the Raman spectra of the flake prior and after placement onto the electrodes. The "2D" peak shows the characteristic multi-band s...

Antenna Enhanced Graphene THz Emitter and Detector

“…In particular, it enables broadband interaction of photons with the two dimensional (2D) atomic layer from the far infrared up to the ultraviolet 3 . This has led to various optoelectronic devices operating with photons in the visible [4][5][6][7] , near infra-red [8][9][10][11] , mid infra-red [12][13][14][15][16] and far infrared [17][18][19][20][21][22][23][24] . Applications of graphene field effect transistors (GFET) in the few terahertz (THz) frequency range are particularly appealing since it's one of the least developed regimes lying in the gap between efficient manipulation with electronics and photonics [25][26][27] .…”

Photothermoelectric and Photoelectric Contributions to Light Detection in Metal–Graphene–Metal Photodetectors

“…Devices were also fabricated for detection of THz light. 28,29 In this low energy range, Pauli blocking forbids the direct excitation of e−h pairs due to finite doping. Instead, an antenna coupled to source and gate of the device excites plasma waves within the channel.…”

Surface Plasmon Polariton Graphene Photodetectors

“…The interference between surface plasmon polaritons and the incident wave introduces new functionalities, such as light flux attraction or repulsion from the contact edges, enabling the tailored design of the photodetector's spectral response. This architecture can also be used for surface plasmon bio-sensing with direct-electricreadout, eliminating the need of complicated optics.Graphene-based photodetectors (PDs) [1,2] have been reported with ultra-fast operating speeds (up to 262GHz from the measured intrinsic response time of graphene carriers [3]) and broadband operation from the visible and infrared [3][4][5][6][7][8][9][10][11][12][13][14][15][16] up to the THz [17][18][19]. The simplest graphene-based photodetection scheme relies on the metal-graphene-metal (MGM) architecture [5,7,8,11,[20][21][22], where the photoresponse is due to a combination of photo-thermoelectric and photovoltaic effects [5,7,8,11,[20][21][22].…”