Publications

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We have fabricated and characterized AlInAsSb- and InPAsSb-absorber nBn infrared detectors with 200 K cutoff wavelengths from 2.55 to 3.25 μm. Minority-carrier lifetimes determined by microwave reflectance measurements were 0.2-1.0 μs in doped n-type absorber materials. Devices having 4 μm thick absorbers exhibited sharp cutoff at wavelengths of 2.9 μm or longer and softer cutoff at shorter wavelengths. Top-illuminated devices with n+ InAs window/contact layers had external quantum efficiencies of 40-50% without anti-reflection coating at 50 mV reverse bias and wavelengths slightly shorter than cutoff. Despite the shallow-etch mesa nBn design, perimeter currents contributed significantly to the 200 K dark current. Dark currents for InPAsSb devices were lower than AlInAsSb devices with similar cutoff wavelengths. For unoptimized InPAsSb devices with 2.55 μm cutoff, 200 K areal and perimeter dark current densities at -0.2 V bias in devices of various sizes were approximately 1x10-7 A/cm2 and 1.4x10-8 A/cm, respectively.

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Here, the design, fabrication, and characterization of an actively tunable long-wave infrared detector, made possible through direct integration of a graphene-enabled metasurface with a conventional type-II superlattice infrared detector, are reported. This structure allows for post-fabrication tuning of the detector spectral response through voltage-induced modification of the carrier density within graphene and, therefore, its plasmonic response. These changes modify the transmittance through the metasurface, which is fabricated monolithically atop the detector, allowing for spectral control of light reaching the detector. Importantly, this structure provides a fabrication-controlled alignment of the metasurface filter to the detector pixel and is entirely solid-state. Using single pixel devices, relative changes in the spectral response exceeding 8% have been realized. These proof-of-concept devices present a path toward solid-state hyperspectral imaging with independent pixel-to-pixel spectral control through a voltage-actuated dynamic response.

An InGaAs/GaAsSb Type-II superlattice is explored as an absorber material for extended short-wave infrared detection. A 10.5 nm period was grown with an InGaAs/GaAsSb thickness ratio of 2 with a target In composition of 46% and target Sb composition of 62%. Cutoff wavelengths near 2.8 μm were achieved with responsivity beyond 3 μm. Demonstrated dark current densities were as low as 1.4 mA/cm2 at 295K and 13 μA/cm2 at 235K at -1V bias. A significant barrier to hole extraction was identified in the detector design that severely limited the external quantum efficiency (EQE) of the detectors. A redesign of the detector that removes that barrier could make InGaAs/GaAsSb very competitive with current commercial HgCdTe and extended InGaAs technology.