Dual origin of room temperature sub-terahertz photoresponse in graphene field effect transistors

Abstract

Graphene is considered as a promising platform for detectors of high-frequency radiation up to the terahertz (THz) range due to graphene ′ s superior electron mobility. Previously it has been shown that graphene field effect transistors (FETs) exhibit room temperature broadband photoresponse to incoming THz radiation thanks to the thermoelectric and/or plasma wave rectification. Both effects exhibit similar functional dependences on the gate voltage and therefore it was found to be difficult to disentangle these contributions in the previous studies. In this letter, we report on combined experimental and theoretical studies of sub-THz response in graphene field-effect transistors analyzed at different temperatures. This temperature-dependent study allowed us to reveal the role of photo-thermoelectric effect, p-n junction rectification, and plasmonic rectification in the sub-THz photoresponse of graphene FETs.Over the last decade, graphene has attracted a considerable attention in the fields of photonics 1 , plasmonics 2 , and optoelectronics 3 . The interest is motivated by graphenes unique gate-tuneable physical properties that allow realization of radiation detectors operating in a wide range of frequencies 4-7 .Electromagnetic radiation in the terahertz (THz) range deserves a special attention as it allows fast and non-destructive imaging of objects with a strong potential in medical and security sectors 8 . With this potential, the development of efficient THz generators and sensitive detectors is an important technological problem.Recently, it has been shown that graphene field-effect transistors (FETs) can act as THz detectors exhibiting a dc photoresponse to impinging radiation 7,[9][10][11][12][13][14][15][16] . A broadband photodetection in the sub-THz range with the responsivity reaching tens of V/W and noise equivalent power of hundreds of pW/Hz 1/2 has been demonstrated in graphene FETs designed in the configuration where the incoming radiation is coupled between the source and the gate terminals 9,10,14,15 . In this configuration, the photoresponse is usually attributed to the so-called Dyakonov-Shur (DS) rectification arising as a result of the plasma waves excitation in the FET channel 17,18 . However, other effects can also impact the photoresponse. For instance, photo-thermoelectric effect (PTE) arising from the temperature gradient in a FET can provide an additional rectification of the incoming high-frequency signal 5,7 . As we show below, both PTE and DS effects exhibit similar functional dependence on the gate voltage and result in the same sign of the photoresponse, that makes it challenging to point to the origin of the observed rectification. Further improvement of graphene-based THz photodetectors requires a deeper understanding of the rectification mechanisms governing the photoresponse.In this work, we analyze the sub-THz photoresponse of graphene-based FET by comparing its responsivity at liquid nitrogen and room temperatures. Such temperaturedependent measurements allowed us to point ...

Thermoelectric graphene photodetectors with sub-nanosecond response times at terahertz frequencies

“…The low thickness of the heterostructures (<45 nm) and of the edge-contacts (∼45 nm) allows us to use a thinner oxide (70 nm) as encapsulating layer before g T deposition ( Figure 1C and D), thus increasing the effective gate-tochannel capacitance per unit area: C g ∼ 100 nF cm −2 for both samples. This parameter is important for THz FET detectors [25], since the responsivity (R v ), a figure of merit defined as the ratio between photovoltage (Δu) and impinging optical power, is typically proportional to the sensitivity of the FET conductance to changes in the gate voltage (V g ) [25].…”

Resonant terahertz detection using graphene plasmons

“…2a). This behaviour is common for this type of devices and is related to additional rectification by p-n junctions at the boundaries between the p-doped graphene channel and the n-doped contact regions 24,31,32 .…”

Response of carbon nanotube film transistor to the THz radiation

“…The responsivity of the device to different frequencies radiation at liquid helium temperature Thus, we showed that FET device with carbon nanotube film as a transport channel detect THz radiation in all temperature ranges. Previously CVD graphene device in the Dyakonov-Shur configuration was shown to have 1V/W responsivity [5] and graphene encapsulated between two slabs of hexagonal boron nitride 20V/W [6]. In comparison with this CNT device shows responsivity up to 100V/W to radiation of THz frequency range.…”