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.

Group III-V wide band gap materials are widely used in developing solar blind, radiation-hard, high speed optoelectronic devices. A device detecting both ultraviolet ͑UV͒ and infrared ͑IR͒ simultaneously will be an important tool in fire fighting and for military and other applications. Here a heterojunction UV/IR dual-band detector, where the UV/IR detection is due to interband/intraband transitions in the Al 0.026 Ga 0.974 N barrier and GaN emitter, respectively, is reported. The UV threshold observed at 360 nm corresponds to the band gap of the Al 0.026 Ga 0.974 N barrier, and the IR response obtained in the range of 8-14 m is in good agreement with the free carrier absorption model.

Terahertz detection using the free-carrier absorption requires a small internal work function of the order of a few millielectron volts. A threshold frequency of 3.2 THz (93 microm or approximately 13 meV work function) is demonstrated by using a 1 x 10(18) cm(-3) Si-doped GaAs emitter and an undoped Al(0.04)Ga(0.96)As barrier structure. The peak responsivity of 6.5 A/W, detectivity of 5.5 x 10(8) Jones, and quantum efficiency of 19% were obtained at 7.1 THz under a bias field of 0.7 kV/cm at 6 K, while the detector spectral response range spans from 3.2 to 30 THz.