QWIP

AlGaAs quantum well infrared photodetector (QWIP) focal planes have achieved sufficient sensitivity out to 10-p.m wavelength to result in scene temperature sensitivity of ca 0.2°C when the focal plane is cooled to 77 K. Spectral sensitivity is shown in Eigure 9c and array information is given in Table 1. The supedattice, a newer tool for achieving controlled activation energy, should present many alternative infrared detection techniques. 

Eig. 13. Absorption between confined energy levels in a quantum well infrared photodetector (QWIP). The energy difference between the... 

See also Gallium entries GaAs-AlGaAs QWIPs, 22 181-182. 

Sivco, and Alfred Y. Cho, Quantum Interference Effects in Intersubband Transitions H. C. Liu, Quantum Well Infrared Photodetector Physics and Novel Devices S. D. Gunapala and S. V. Bandara, Quantum Well Infrared Photodetector (QWIP) Focal Plane Arrays... 

Fig. 13. Absorption between confined energy levels in a quantum well infrared photodetector (QWIP). The energy difference (E —E ) between the confined energy levels in a quantum well may be designed such that it is resonant with ir radiation. The band gap, E is much greater, therefore direct band...

S. D. Gunapala and S. V. Bandara, Quantum Well Infrared Photodetector (QWIP) Focal Plane Arrays... 

FLIR devices can be divided in two classes by their detecting waveband. Mid-IR detectors, like the StarSAFIRE series mentioned above, are commonly used in humid environments since they show less signal depression by water vapour. However the detection of oil spills shows variable results and is not favourable as a stand-alone sensor for this purpose. Long-IR detectors (8-14 pm, sometimes realised by QWIP detectors with smaller... 

Quantum Well IR Photodetector (QWIP) Intraband photoexcitation of electrons horn confined states in the conduction band of quantum wells into the continuum... 

The newest and perhaps most versatile of the detectors shown is the QWIP array. QWIP detectors are made from gallium arsenide (GaAs) material. These detectors are narrow-band, high-speed, high-sensitivity detectors that can be designed to operate in selected narrow bands from the MWIR (2-5 pm) to the LWIR (8-14 pm). The versatility of this detector, as well as others, will be illustrated in the applications chapters in Part II of this text. 

For special applications where high speed, improved sensitivity, or spectral selectivity is required, cooled photodetector arrays are used. These include PtSi, InSb, HgCdTe, and most recently GaAs QWIPs, all of which require cooling. The spectral response characteristics of these detectors are illustrated in Fig. 2.16. 

For special applications involving high-speed phenomena, high-thermal sensitivity, and processing flexibility at longer wavelengths, the detector of choice has become the GaAs QWIP FPA. 

Spatial resolution 1.1 milliradian (320 x 240 element GaAs QWIP FPA) Frame repetition rate selectable from 50/60 Hz to 750/900 Hz... 

AIM pCam, FS, HuntIR, and FL FLIR Families Modular, building block cameras using cooled HgCdTe, GaAs QWIP and PtSi FPAs from 128 x 128 element to 640 X 486 element. 

Sapphire, Ultra, and Star series Multipayload packaged systems for commercial and military applications featuring high resolution Stirling-cycle-cooled InSb FPA (3-5 pm) and QWIP FPA (8-9 pm) detectors. (FLIR offers many other security and surveillance-related products described on its website). 

Early devices using lattice-engineered materials were referred to as quantum well infrared photodetectors (QWIPs), then as quantum dot infrared photodetectors (QDIPs), but now it is difficult to separate them from other natural materials. 

Rehm (2001) Responsivity and Gain in InGaAs/GaAs-QWIPs and GaAs/ AlGaAs-QWIPs A Comparative Study by R. Rehm, H. Schneider, K. Schwarz, M. Walther, P. Koidl, and G. Weimann. Proc. SPIE 1488, 379-385. 

X 256, 25 pm pitch two-color QWIP EPA operating at > 70K (MW/LW) and > 65K (LW/LW). Data include graphs of spectral response curves and dark current vs bias. 

Trager (2012) Springer Handbook of Lasers and Optics (2nd edition) by F. Trager, ed. Springer Science -F Business Media LLC New York (2007). See especially p. 529. Typical photoconductor gains for QWIPS are 0.1 to 1.0, though values... 

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