Reduced Dark Current With a Specific Detectivity Advantage in Extended Threshold Wavelength Infrared Detector

Reduced dark current leading to a specific detectivity (D*) advantage over conventional detectors for extended threshold wavelength (ET) detectors are reported in this article. For an infrared (IR) detector with a graded injector barrier and barrier energy offset, the measured dark current was found to agree well with theoretical fits obtained from a 3-D carrier drift model using the designed value of Δ $=$ 0.40 eV $(\boldsymbol{\lambda}_{t}$ $=$ 3.1 $\boldsymbol{\mu}$ m) (where Δ $=$ 1.24/ $\boldsymbol\lambda_{t}$ , Δ is the internal work function and $\lambda_{t}$ is the corresponding threshold wavelength), whereas the effective photoresponse threshold wavelength determined from the spectral response measurements corresponds to 13.7  ${\boldsymbol{\mu}}$ m at 50 K. However, for the conventional detectors, both the dark current and photoresponse threshold agree very well with the designed value of Δ. Comparing threshold wavelengths of an ET detector and a conventional detector, an advantage in D* is observed for ET detectors due to the strong reduction in dark current. Using this idea, standard threshold semiconductor detectors could be designed to operate as long wavelength detectors with a higher value of detectivity and dark current (corresponding to the original short-wavelength threshold).