Nonlinear photoconductivity effects at high excitation power in quantum well infrared photodetectors (QWIPs) are studied both experimentally and theoretically. The photoconductivity nonlinearity is mainly caused by a redistribution of the electric potential at high power, which leads to a decrease of electric field in the bulk of the QWIP. As a result of the decreased field, the photoexcited electron escape probability and drift velocity decrease resulting in a decrease of responsivity.

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.

Photoconductive gain and generationrecombination noise in quantum well infrared photodetectors

Heterojunction interfacial work function internal photoemission detectors were used to demonstrate infrared response originating from hole transitions between light/heavy hole bands and the split-off (spin-orbit) band. A GaAs∕AlGaAs heterojunction with a threshold wavelength of ∼20μm indicated an operating temperature of 130K for split-off response in the range of 1.5–5μm with a peak D* of 1.0×108 Jones. Analysis suggests that practical devices with optimized parameters are capable of achieving room temperature operation with higher specific detectivity. Possible approaches to tailor the threshold for the split-off response to different wavelength ranges using different materials such as phosphides and nitrides are also discussed.

Results are presented on the performance of a heterojunction interfacial workfunction internal photoemission (HEIWIP) wavelength-tailorable detector. The detection mechanism is based on free-carrier absorption in the heavily doped emitter regions and internal emission across a workfunction barrier caused by the band gap offset at the heterojunction. The HEIWIP detectors have the high responsivity of free-carrier absorption detectors and the low dark current of quantum well infrared photodector type detectors. For a 70±2 cutoff wavelength detector, a responsivity of 11 A/W and a D*=1×1013 cmHz/W with a photocurrent efficiency of 24% was observed at 20 μm. From the 300 K background photocurrent, the background limited performance (BLIP) temperature for this HEIWIP detector was estimated to be 15 K. This HEIWIP detector provides an exciting approach to far-infrared detection.