Sub-Micron Area Heterojunction Backward Diode Millimeter-Wave Detectors With 0.18 ${\rm pW/Hz}^{1/2}$ Noise Equivalent Power

InAs/AlSb/AlGaSb heterojunction backward diodes are promising detectors for millimeter-wave imaging applications due to their high sensitivity, low noise, and high cutoff frequency. By using a device heterostructure with a thin (11 Å) barrier layer, δ-doped cathode, and optimized Al_xGa_1-xSb anode composition (x=12%), in conjunction with submicron (0.4×0.4 μm²) active area, fabricated detectors have demonstrated DC curvatures of -47 V^-1 and record unmatched sensitivities of 4600 V/W at 94 GHz. Impedance-matched sensitivities of 49,700 V/W at 94 GHz are projected from on-wafer S-parameter and sensitivity measurements. These detectors have measured junction resistances of 814 Ω·μm² and capacitances of 15 fF/μm². A record low NEP_min of 0.18 pW/Hz^1/2 has been projected under conjugate matching conditions. This study demonstrates the potential of Sb-heterostructure backward diodes as ultra-low-noise millimeter-wave direct detectors.