Recent intense electrical and optical studies of graphene have pushed the material to the forefront of optoelectronic research. Of particular interest is the few terahertz (THz) frequency regime where efficient light sources and highly sensitive detectors are very challenging to make. Here we present THz sources and detectors made with graphene field effect transistors (GFETs) enhanced by a double-patch antenna and an on-chip silicon lens. We report the first experimental observation of 1-3 THz radiation from graphene, as well as four orders of magnitude performance improvements in a GFET thermoelectric detector operating at ~2 THz. The quantitative analysis of the emitting power and its unusual charge density dependence indicate significant non-thermal contribution from the GFET. The polarization resolved detection measurements with different illumination geometries allow for detailed and quantitative analysis of various factors that contribute to the overall detector performance. Our experimental results represent a significant advance towards practically useful graphene THz devices. Subject terms: Physical sciences, Materials science, Condensed matter3 Manuscript textThe gapless electronic structure of graphene 1 is a unique property that has drawn significant attention from both basic sciences and practical applications 2 . 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 4-7 , 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] . Here we perform combined THz emission-detection measurements using devices made with monolayer graphene. Our results represent the first study of THz emission from graphene, as well as significant improvements in GFET thermoelectric THz detectors.A common bottleneck in graphene photonic and optoelectronic devices is the limited light-matter interaction, because of the 2D crystal's sub-nanometer thickness.This has led to the 'greybody' radiation 28,29 range that is notoriously difficult to work with. For the emitter, we observe a radiated power that is significantly larger than the anticipated thermal radiation, suggesting additional radiation channels at our disposal for devising efficient graphene THz sources.For the detector, we achieve four orders of magnitude sensitivity improvements, which, in conjunction with its high speed 19,20 , makes the GFET a strong competitor to other contemporary THz sensors.The antenna is designed to have a size of 45×31 µm 2 as shown in Fig.1 indicates an optimal operation frequency of 2.1THz. The electric field distribution at ...

thermoelectric [ 5,6 ] and photovoltaic [ 7 ] single wall carbon nanotubes (SWCNT) IR detectors shows good performance, but such detectors require asymmetric fabrication processes that are much more complex than what we describe in this paper. Fabrication of bolometric detectors is fairly straightforward and these can conveniently operate at room temperature. The functioning principle behind a bolometric CNT IR sensor involves incident radiation heating the CNT network, resulting in a measurable change in the CNT's electrical resistance since the resistance of CNTs strongly depends on the temperature. Therefore, reducing the CNT fi lm's thermal link to the environment is necessary to obtain an enhanced bolometric photoresponse. [ 1,8 ] For effi cient bolometer operation, the radiation absorber should have a large absorptivity, low heat capacity, and adequate temperature coeffi cient of resistance. [ 8 ] The very low density, high surface area and negligible heat capacity of CNTs make them very responsive as they are very sensitive to incident radiation. Accordingly, little absorption is needed to heat individual nanotubes and give a measurable response. The bolometric detectors require a bias voltage to generate a photoresponse whereas photovoltaic and thermopile detectors can operate under zero voltage. [ 6,9 ] CNT-based bolometric IR detectors can be broadly categorized into two groups: i) SWCNT-polymer composite fi lms where SWCNTs are uniformly embedded in polymer matrix [10][11][12][13][14] and ii) suspended SWCNT/MWCNT networks or individual bundles prepared by chemical vapor deposition (CVD) or vacuum fi ltration transfer. [ 1,8,[15][16][17][18] Recently, the bolometric characteristics of CNT-polystyrene composite fi lms were examined and a responsivity of 500 V/W and response time of around 200 ms for the composite IR sensor were observed. [ 12 ] Several similar reports on IR sensors based on CNT-polymer composite fi lms show response times on the order of hundreds of milliseconds. [10][11][12][13][14] Slower response time and complex sensor fabrication methods unsuitable for large volume fabrication are the major draw backs of CNT-polymer composite IR sensors and printed MWCNT IR sensors [ 19 ] on plastic. A plastic CNT sensor with the incorporation of an absorber and a refl ector for better sensor performance has also been reported. [ 20 ] Suspending CNTs in air or vacuum has been shown to reduce their thermal link to the environment leading to significant enhancement of the bolometric photoresponse. [ 1,8,[15][16][17][18]

We have measured the noise performance and gain bandwidth of 35 Å thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. The best double-sideband receiver noise temperature is less than 1300 K with a 3 dB bandwidth of ≈5 GHz. The gain bandwidth is 3.2 GHz. The mixer output noise dominated by thermal fluctuations is 50 K, and the intrinsic conversion gain is about −12 dB. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K.

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