Quantum Well and Quantum Dot Based Detector Arrays for Infrared Imaging
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Quantum Well and Quantum Dot Based Detector Arrays for Infrared Imaging Sarath Gunapala, Sumith Bandara, Cory Hill, David Ting, John Liu, Jason Mumolo, Sam Keo, and Edward Blazejewski Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109 ABSTRACT Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 320x256 pixel quantum well infrared photodetector (QWIP) dualband focal plane arrays (FPAs) have been demonstrated with excellent imagery. Currently, we are developing a 1024x1024 pixel simultaneous pixel co-registered dualband QWIP FPA. In addition, epitaxially grown selfassembled InAs/InGaAs/GaAs quantum dots (QDs) are exploited for the development of largeformat FPAs. The Dot-in-a-Well (DWELL) structures were experimentally shown to absorb both 45o and normal incident light, therefore a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 microns, with peak detectivity reaching ~ 1 x 1010 Jones at 77 K. The devices were fabricated into the first LWIR 640x512 pixel QDIP FPA, which has produced excellent infrared imagery with the NETD of 40 mK at 60K operating temperature. INTRODUCTION There are many applications that require mid-wavelength infrared (MWIR) and longwavelength infrared (LWIR) dualband focal plane arrays (FPAs). For example, a dualband FPA camera would provide the absolute temperature of a target with unknown emissivity, which is extremely important to the process of identifying a temperature difference between missile targets, warheads, and decoys. Dualband infrared FPAs can also play many important roles in Earth and planetary remote sensing, astronomy, etc. Furthermore, monolithically integrated pixel collocated simultaneously readable dualband FPAs eliminate the beam splitters, filters, moving filter wheels, and rigorous optical alignment requirements imposed on dualband systems based on two separate single-band FPAs or a broadband FPA system with filters. Dualband FPAs also reduce the mass, volume, and power requirements of dualband systems. Due to the inherent properties such as narrow-band response, wavelength tailorability, and stability (i.e., low 1/f noise) associated with GaAs based QWIPs [1-6], it is an ideal candidate for large format dualband infrared FPAs. 320X256 PIXEL DUALBAND FOCAL PLANE ARRAY As shown in figure 1, our dualband FPA is based on two different types of (i.e., MWIR and LWIR) QWIP devices separated by a 0.5 micron thick, heavily doped, n-type GaAs layer. The device structures of the MWIR and LWIR devices are very similar to the MWIR and LWIR The MWIR device described here, each period of the multi-quantum-well (MQW) structure consists of coupled quantum wells of 40 Å containing 10 Å GaAs, 20 Å In0.3Ga0.7As, and 10 Å GaAs layers (doped n = 1x1018 cm–3) and a 40 Å undoped barrier of Al0.3Ga0.7As between coupled quantum wells, and a 400 Å thick undoped barrier of Al0.3Ga0.7As. Each period of the
LWIR MQW structure consists of quantum
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