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We describe the concept of the submonolayer quantum dot infrared photodetector (SML QDIP) and report experimental device results on long-wavelength infrared detection. An SML QDIP structure was fabricated into megapixel focal plane arrays, which produced clear infrared images up to 80 K. Detectors in the focal plane showed a responsivity peak at 7.8 μm and noise equivalent temperature difference of 33 mK at 70 K.

The feasibility of an all molecular-beam epitaxially (MBE) grown, bias-switchable, dual-band HgCdTe detector is demonstrated. Detection in the midwavelength infrared (MWIR) band only or the long-wavelength band (LWIR) only is accomplished by the proper selection of detector bias in the ≥±100 mV range. The devices were all grown in situ by the MBE on CdZnTe or GaAs substrates and consisted of three intentionally doped layers in an n–p–n sequence. At 77 K the floating base two terminal devices responded to the ∼4.9–8 μm spectral band with the application of ≥−100 mV to the bottom contact and to the ∼2.1–4.9 μm band with the application of ≥0 mV. Quantum efficiency depended on bias with a maximum of 59% for LWIR and 66% for MWIR wavelengths at −150 mV and ≥0 mV, respectively. The operation of the dual-band detector is discussed. Significant design differences between the heterojunction phototransistor and the dual-band detector are noted.

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This stJdy investigates the separate dark current components which are dom'nanr in the diffus'on-limited regime in MWIR n/p HgCdTe/CdTe/sapphire photodetectors. Both mesa and p.anar configurations of variable-area diodes were fabr:cated and evaluated over the temperatJre range from 78 to 250 K. Simple analytical express'ons are Jsed to calculate tne contributions of bulk, lateral and surface effects from the perimeterlarea aependence of R+l and measurement of the minority carr:er d:ffusion length. The analysis ind'cates that at 180 K the nesa diode results can oe accounted for oy bulk and lateral currents, but that the planar diodes are limiteo oy surface currents. The 780 r( median &A for the mesa jiodes ranges from 63 R cm2 for 500 x 500 pm2 d:ooe areas to 14 R cm2 for .30 x 30 pm2 aiodes at a cut-off wavelength of 4.64 pm. Scann'ng laser m'croscope neasuements determine the 180 K e ectron minority carrier diffus:on length to be 17-18um.

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