A Novel InSb Photodiode Infrared Sensor Operating at Room Temperature
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A Novel InSb Photodiode Infrared Sensor Operating at Room Temperature Koichiro Ueno, Edson G. Camargo, Yoshifumi Kawakami, Yoshitaka Moriyasu, Kazuhiro Nagase and Naohiro Kuze Central R&D Laboratories, Asahi Kasei Corporation, 2-1 Samejima, Fuji, Shizuoka 416-8501, Japan E-mail: [email protected] ABSTRACT A microchip-sized InSb photodiode based infrared sensor (InSb PDS) that operates at room temperature was developed. The InSb PDS consists of 700 photodiodes connected in series and consumes no powe r, because it works in photovoltaic mode to output an open-circuit voltage. The InSb PDS has a typical responsivity of 1,900 V/W and an output noise of 0.15 µV/Hz1/2. A detectivity of 2.8x108 cmHz1/2 /W was obtained at 300 K. The InSb PDS has performance high enough for applications such as mobile electronic equipment, personal computers, and consumer electronics. INTRODUCTION To detect weak infrared irradiation, like that from a human body, pyroelectric sensors are generally used due to their high sensitivity at room temperature. However, they require the use of metallic packages to insulate the sensitive element from thermal disturbances and electromagnetic noise, making their miniaturization difficult. Moreover, a pyroelectric sensor cannot easily detect a stationary human body because the surface charge generated on the pyroelectric element disappears gradually if the body is stationary. Existing InSb photodetectors must be used with cooling systems to reduce the influence of high intrinsic carrier density, which is around 2x1016 cm-3. An InAsSb heterojunction photodiode that operates near room temperature has also been reported [1-3]. However, its responsivity is limited by the Auger generation and recombination process, which makes the photo-generated signal difficult to amplify using conventional amplifiers. An AlInSb barrier layer was proposed to suppress the Auger processes by decreasing the free carrier concentration to below its equilibrium value [4]. However, Auger-suppressed non-equilibrium photodiodes suffer from 1/f noise; hence, high detectivity could only be obtained at high frequencies [5]. To avoid 1/f noise, we operated our InSb photodiode in photovoltaic (zero bias) mode to output an open-circuit voltage. We found not only an increase in resistance at zero bias but also that the photocurrent was higher when an
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AlInSb barrier layer was inserted. In addition, to improve performance, several micron-sized photodiodes were serially connected to each other. As a result of this improvement, we obtained an output voltage level that can be amplified by a standard CMOS integrated circuit. Serially connected HgCdTe photovoltaic detectors have also been reported [6]. However, HgCdTe suffers from instability problems due to the high vapor pressure of Hg. As our InSb PDS operates in a photovoltaic mode, no thermal insulation is required, allowing its miniaturized plastic molding. EXPERIMENTAL The structure and band diagram of our single InSb photodiode are shown in Figu
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