We report on ultrahigh sensitive, broadband terahertz (THz) detectors based on asymmetric double-grating-gate (A-DGG)
high electron mobility transistors, demonstrating a record responsivity of 2.2 kV/W at 1 THz with a superior low
noise equivalent power of 15 pW/√Hz using InGaAs/InAlAs/InP material systems. When THz radiation is absorbed
strong THz photocurrent is first generated by the nonlinearity of the plasmon modes resonantly excited in undepleted
portions of the 2D electron channel under the high-biased sub-grating of the A-DGG, then the THz photovoltaic response
is read out at high-impedance parts of 2D channel under the other sub-grating biased at the level close to the threshold.
Extraordinary enhancement by more than two orders of magnitude of the responsivity is verified with respect to that for
a symmetric DGG structure.
Sensitive water concentration mapping in thin animal tissue samples has been demonstrated using tunable
monochromatic THz-wave parametric source. A novel sample preparation approach is performed to effectively preserve
tissue freshness at room temperature. The time course results show the sample characteristic of water content and
distribution can be well measured and excellently repeated in 70minutes with a standard deviation of less than 1%. These
results suggest the method of water volume concentration and distribution measurement using THz-wave has good
stability with proper sample preparation, which has great potential in the fields of medical and biological diagnosis.