Fig. 1. Design of the epitaxial IR-millimeter/THz wave multiband photodetector. (a) Structure of the epitaxial InSb on GaAs. (b) Relative permittivity of InSb in the millimeter/terahertz wave range followed by a Drude model. (c) Schematic of the multiband detector. A planar log-period antenna is adopted to couple the millimeter/terahertz wave. IR wave impinges on the surface of the InSb mesa. Inset is the microscope image of the detector and the scale bar represents 50 μm. (d) Typical field distribution by the couple of the antenna calculated by Ansys HFSS software. In the Ansys HFSS antenna simulation, the electromagnetic wave is fed at the gap with an impedance of 50 Ω. (e) E plane and H plane of the antenna. (f) Typical distribution of |E|2 near the central Au-InSb-Au structure calculated by COMSOL Multiphysics software. PML boundary condition is adopted in the simulation. The incident light is polarized along the direction of the y axis to meet the experiments. Distribution of |E|2 along (g) the cut-line I and (h) the cut-line II in (f).

Fig. 2. Dark current and noise of the detector. (a) Current–voltage (I–V) characteristic curves of the detector at temperatures from 293 to 170 K. (b) Calculated voltage noise of the detector with respect to bias at different temperatures.

Fig. 3. Characterization of the detector for IR wave detection. (a) Relative spectral response of the detector at different temperatures. (b) Blackbody responsivity of the detector with respect to bias at different temperatures. (c) Blackbody responsivity of the detector at different temperatures under an applied voltage bias of 1000 mV. (d) Blackbody detectivity of the detector with respect to bias at different temperatures. (e) Blackbody detectivity of the detector at different temperatures under an applied voltage bias of 1000 mV.

Fig. 4. Response speed of the detector for IR. (a) Typical response waveform of the detector under illumination of a 2.94 μm laser with rise time of 20 ns. (b) Normalized amplitude frequency response of the detector.

Fig. 5. Characterization of the detector at 0.270 THz. (a) Responsivity and NEP of the detector with respect to bias at 0.270 THz. (b) Responsivity and NEP of the detector with respect to temperature under an applied voltage bias of 1000 mV.

Fig. 6. Multispectral response of the detector for a millimeter/terahertz wave under an applied bias of 1000 mV. (a) Responsivity. (b) NEP. Performances of three commercial VDI modules are also plotted for comparison.

Fig. 7. Response speed of the detector for a millimeter/terahertz wave. (a) Normalized amplitude frequency response of the detector at 0.270 THz at different temperatures. (b) The f−3dB value and corresponding rise time of the detector derived from (a).