Fig 1

(a) Schematic diagram of an antenna integrated graphene THz detector. hBN-encapsulated graphene is predefined to 'H-shaped'. The left and right parts of antenna are used as left and right top gates to create a pn junction 25. (b) Side view of the device design. The gap between left and right parts of the antenna is 800 nm. Top gate dielectric consists of 20 nm HfO2 and 30 nm hBN. (c) Optical image of the as-fabricated THz detector. The scale bar is 10 μm. (d) Correlation between the G and 2D peaks in graphene Raman spectrum. The red and blue dashed lines indicate the axes of strain and doping. The data shows the low doping, and little compression strain. The full width at half maximum (FWHM) of 2D peak is about 25 cm−1 as shown by colorbar, which confirms that the graphene in the channel is single layer. The inset shows a typical Raman spectrum of the SLG. (e) THz photocurrent map of the detector. The map is obtained by scanning the detector on the focal plane and recording the photocurrent. The parameters are Pin = 0.9 mW, VL = −2 V, and VR = 0.4 V. White dotted lines indicate the outline of the device. The scale bar is 500 μm. (f) Same map as panel (e) but shown in three-dimensional contour. The inset shows line cuts at the max point along X and Y directions (blue and red, respectively)."

Fig 2

(a) Simulated dependence of enhanced electric field on the half-length L of antenna. Parameters are f = 2.7 THz, gap between two antenna parts Lgap = 800 nm, polarization parallel to antenna axis, as shown by the black arrow. Two peaks correspond to λ/4 and 3λ/4 resonances (λ = 110 μm) whose electric-field distributions are shown as insets. (b) Simulated enhancement of the electric field as a function of radiation frequency. The optimal operating frequency is around 2.7 THz. Parameters: L = 25 μm, Lgap = 800 nm, polarization is shown by black arrows. (c) Simulated dependence of electric-field enhancement on the antenna gap. (d) Simulated spatial distribution of field enhancement at antenna. The scale bar is 10 μm. (e) Experimental dependence of photocurrent on polarization. 0° and 180° correspond to polarizations parallel with the antenna axis. The ratio between photocurrent at parallel and perpendicular polarizations Iph///Iph⊥ is between 27 to 295. (f) Polar plot data in panel (e) with red line as simulated curve."

Fig 3

(a) Dependence of Resistance R on charge carrier density. (b) Dependence of photoresponsivity (ℜph) and seebeck coefficient. By keeping one gate voltage constant, ℜph shows similar trend as seebeck coefficient of channel under the other gate. SL and SR are seebeck coefficients of graphene under left and right top gates. (c) Change curve of device photocurrent responsivity ℜph (solid red line) and seebeck coefficient SR (solid black line), where VL = −1 V. (d) Dependence of R on two top gate voltages. Dashed line indicate data in panel (a). (e) Dependence of ℜph on two top gate voltages. Solid and dashed lines indicate data in panel (b) and (c), respectively. Radiation parameters: f = 2.7 THz, power Pin = 0.9 mW, polarization parallel to the antenna axis. (f) The noise equivalent power (NEP), estimated from data in panel (d) and (e)."