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
_x
Ga
_1-x
Sb anode composition (x=12%), in conjunction with submicron (0.4×0.4 μm
²
) 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·μm
²
and capacitances of 15 fF/μm
²
. 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.