This paper reviews recent advancements in the research of THz detection by an asymmetric dual-grating gate structure epitaxial-graphene-channel field effect transistor (ADGG-EG-FETs). We designed and fabricated ADGG-EGFET for plasmonic (PL) detection, and it performed a high sensitivity and fast response to irradiated THz with 0.95 THz. The behavior of measured dependence on gate bias voltage cannot be explained only by the PL effect. We found such a phenomenon as a new current-driven phototermoelectric (PTE) detection assisted by electrostatic carrier drift/diffusion under the application of DC drain biases. Furthermore, we analyze the response speed of our fabricated detector to reveal the transition point between PL and PTE detection mechanisms. The minimum output pulse width was ~190 ps when one ADGG bias was at the Dirac voltage (i.e., charge neutrality point) to promote the PL detection, whereas the pulse width was ~200 ps when both ADGG biases were at well-doped levels to promote the PTE detection. Compared with the input pulse width of 155 ps, the intrinsic response time of the detector was estimated to be 10 ps for the PL and 20 ps for the PTE detection. This can be quantitatively explained by the characteristic relaxation times of the momentum relaxation for the PL, and the energy relaxation of the hot electrons by optical-phonon emission for the PTE detection. These results indicate that the ADGG-EG-FETs THz detectors are promising for applications in 6G to 7G-class THz wireless communication systems.
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