We report a three-color InAs/InGaAs quantum-dots-in-a-well detector with center wavelengths at ∼3.8, ∼8.5, and ∼23.2 μm. We believe that the shorter wavelength responses (3.8 and 8.5 μm) are due to bound-to-continuum and bound-to-bound transitions between the states in the dot and states in the well, whereas the longer wavelength response (23.2 μm) is due to intersubband transition between dot levels. A bias-dependent activation energy ∼100 meV was extracted from the Arrhenius plots of the dark currents, which is a factor of 3 larger than that observed in quantum-well infrared photodetectors operating at comparable wavelengths.

Avoiding cryogenic cooling not only reduces the cost and weight but also simplifies the infrared detector system allowing widespread usage. Here an uncooled infrared detection using intravalence bands is reported. A set of three p-GaAs/ Al x Ga 1−x As multiple heterojunction detector structures were used to demonstrate the concept experimentally. A preliminary detector showed peak responsivity of 0.29 mA/ W at 2.5 m at 300 K. The intravalence band approach can be used to cover various wavelength ranges by using different material systems giving rise to the possibilities of a dual band detector operating in atmospheric windows.

A heterojunction interfacial work function internal photoemission ͑HEIWIP͒ detector with a threshold frequency ͑f 0 ͒ of 2.3 THz ͑ 0 = 128 m͒ is demonstrated. The threshold limit of ϳ3.3 THz ͑92 µm͒ due to the Al fraction being limited to ϳ0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0 kV/ cm are 7.3 A / W, 29%, 5.3ϫ 10 11 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60°field of view was observed for a bias field of 0.15 kV/ cm. The f 0 could be further reduced toward ϳ1 THz regime ͑ϳ300 m͒ by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.

Heterojunction interfacial work function internal photoemission (HEIWIP) detectors provide an interesting approach to the development of quantum detectors for the terahertz range. In this letter, the cutoff frequency/wavelength variation of HEIWIP detectors having different Al fractions in AlGaAs/GaAs structures is experimentally verified, and a model is presented for designing the structures. A key feature of HEIWIP responsivity is the ability to cover a broad frequency range in a single detector with cutoff tailorability by adjusting the Al fraction in the barrier regions. Extending the response to lower frequencies by the use of AlGaAs emitters and GaAs barriers is also discussed.

Design, modeling, and optimization principles for GaAs/ AlGaAs heterojunction interfacial workfunction internal photoemission (HEIWIP) infrared detectors for a broad spectral region are presented. Both n-type and p-type detectors with a single emitter or multiemitters, grown on doped and undoped substrates are considered. It is shown that the absorption, and therefore responsivity, can be increased by optimizing the device design. Both the position and the strength of the responsivity peaks can be tailored by varying device parameters such as doping and the thickness. By utilizing a resonant cavity architecture, the effect of a buffer layer on the response is discussed. Model results, which are in good agreement with the experimental results, predict an optimized design for a detector with a peak response of 9 A / W at 26 m with a zero response threshold wavelength 0 = 100 m. For a 0 =15 m HEIWIP detector, background limited performance temperature (BLIP temperature), for 180°field of view (FOV) is expected around 80 K. For a 0 =70 m optimized design, a highly doped n-type substrate could increase the peak detectivity from 1.7ϫ 10 10 to 3.4ϫ 10 10 Jones at a FOV= 180°operated at temperatures below T Ͻ T BLIP =13 K. Intrinsic response times on the order of picoseconds are expected for these detectors.