We report high-temperature ͑240-300 K͒ operation of a tunneling quantum-dot infrared photodetector. The device displays two-color characteristics with photoresponse peaks at ϳ6 m and 17 m. The extremely low dark current density of 1.55 A / cm 2 at 300 K for 1 V bias is made possible by the tunnel filter. For the 17 m absorption, the measured peak responsivity is 0.16 A / W ͑300 K͒ for a bias of 2 V and the specific detectivity D * is 1.5ϫ 10 7 cm Hz 1/2 /W ͑280 K͒ for a bias of 1 V. Excellent performance characteristics are also measured for the 6 m photoresponse.

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.

Quantum dot infrared photodetectors (QDIPs) have emerged as attractive devices for sensing long wavelength radiation. Their principle of operation is based on intersublevel transitions in quantum dots (QDs). Three-dimensional quantum confinement offers the advantages of normal incidence operation, low dark currents and high-temperature operation. The performance characteristics of mid-infrared devices with three kinds of novel heterostructures in the active region are described here. These are a device with upto 70 QD layers, a device with a superlattice in the active region, and a tunnel QDIP. Low dark currents (1.59 A cm −2 at 300 K), large responsivity (2.5 A W −1 at 78 K) and large specific detectivity (10 11 cm Hz 1/2 W −1 at 100 K) are measured in these devices. It is evident that QDIPs will find application in the design of high-temperature focal plane arrays. Imaging with small QD detector arrays using the raster scanning technique is also demonstrated.

The characteristics of a tunnel quantum dot intersublevel photodetector, designed for the absorption of terahertz radiation, are described. The absorption region consists of self-organized In 0.6 Al 0.4 As/ GaAs quantum dots with tailored electronic properties. Devices exhibit spectral response from 20 to 75 m ͑ϳ4 THz͒ with peak at ϳ50 m. The peak responsivity and specific detectivity of the device are 0.45 A / W and 10 8 cm Hz 1/2 / W, respectively, at 4.6 K for an applied bias of 1 V. Response to terahertz radiation is observed up to 150 K.

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.