Quantum Dot Long-Wavelength Detectors
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Quantum Dot Long-Wavelength Detectors Pallab Bhattacharya, Adrienne D. Stiff-Roberts, Sanjay Krishna1, and Steve Kennerly2 Solid State Electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan Ann Arbor, MI 48109-2122, U.S.A. 1 Center for High Technology Materials, Department of Electrical Engineering and Computer Engineering, University of New Mexico Albuquerque, NM 87106, U.S.A. 2 Sensors and Electron Devices Directorate, U. S. Army Research Laboratory Adelphi, MD 20783, U.S.A. ABSTRACT Long-wavelength infrared detectors operating at elevated temperatures are critical for imaging applications. InAs/GaAs quantum dots are an important material for the design and fabrication of high-temperature infrared photodetectors. Quantum dot infrared photodetectors allow normal-incidence operation, in addition to low dark currents and multispectral response. The long intersubband relaxation time of electrons in quantum dots improves the responsivity of the detectors, contributing to better hightemperature performance. We have obtained extremely low dark currents (Idark = 1.7 pA, T = 100 K, Vbias = 0.1 V), high detectivities (D* = 2.9x108 cmHz1/2/W, T = 100 K, Vbias = 0.2 V), and high operating temperatures (T = 150 K) for these quantum-dot detectors. These results, as well as infrared imaging with QDIPs, will be described and discussed.
INTRODUCTION Infrared detection is important in a variety of fields, such as military targeting and tracking, law enforcement, environmental monitoring, and space science. Quantum dot infrared photodetectors (QDIPs) have been widely investigated during the past few years for operation in the mid-wavelength (3-5 µm) and long-wavelength (8-14 µm) infrared ranges [1-13]. Three of the major advantages expected from QDIPs over other existing technologies are; (i) normal incidence operation, eliminating the need for external gratings and optocouplers [5,8,10], (ii) high-temperature operation, eliminating the need for expensive cooling systems presently used with mercury cadmium telluride (MCT) detectors [14,15] and quantum well infrared photodetectors (QWIPs) [16,17], and (iii) decreased dark current, increasing the background-limited performance (BLIP) of the detector. Since InAs/GaAs quantum dots are grown by molecular beam epitaxy (MBE) using the mature III-V technology, they are essentially defect-free and do not suffer from the etch-pit densities and void defects that plague MCT detectors. The main disadvantage of the QDIP is the large inhomogeneous linewidth of the quantum dot ensemble due to random variation of dot size in the Stranski-Krastanow growth mode. Despite such challenges, QDIPs are expected to perform better at higher temperatures, especially when compared to QWIPs, due to the increased intersubband relaxation time between the phonon-decoupled ground state and excited states, increasing H3.2.1
the probability that a photoexcited carrier will be collected as photocurrent [9,18-20]. This long intersubband relaxation time in quantum dot
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