A multi-color CdS/ZnSe quantum well photodetector for mid- and long-wavelength infrared detection N. Sfina, N. Zeiri, S. Abdi-Ben Nasrallah n , M. Said Laboratoire de la Matière Condensée et des Nanosciences (LMCN), Département de Physique, Faculté des Sciences de Monastir, 5019 Monastir, Tunisia article info Keywords: II–VI Semiconductors Quantum well devices Intersubband transition Absorption coefficient Infrared photodetector Dark current abstract In this paper, we report on the design and characterization of a quantum well based infrared photodetectors covering simultaneously infrared radiation within mid- and long- infrared spectral regions. The proposed infrared photodetectors rely on intersubband transitions in asymmetric ZnSe/CdS double quantum wells. The three-energy-level and the wavelengths of the intersubband transitions in the asymmetric double quantum wells are obtained by solving the Schrödinger and Poisson equations self consistently, the influence of the right well width on the absorption coefficient is studied. The peak positions of intersubband absorption coefficients in the structure are found at 3.31, 4.4 and 13.5 mm for a 1 nm right well width while the absorption peak positions are located at 3.33, 6.43 and 6.95 mm for a 1.4 nm right well thickness. Then, the electro-optic performances of the infrared photodetector are evaluated; the dark current dependence with the applied voltage and temperature is discussed. This work demonstrates the possibility of detection of widely separated wavelength bands using intersubband transitions in quantum wells with a low dark current. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Recent commercial and military applications have required photodetectors with high sensitivity and multi- spectral ability for detection [1]. Therefore, there is a great interest in quantum well infrared photodetectors (QWIP) in recent years which offer multicolor detection capability in the near- (NIF), mid-wave (MWIR) and long-wave infrared (LWIR) spectral regions [2–5]. The main advantage of such system lies in the fact that devices can be tailored over a wide range by varying the thickness of the constituent materials, their composition and the geometry of wells. One of approaches to reach this spectral range is the use of intersubband and interband transitions in square quan- tum wells (QWs) under high bias to allowing transitions between bound states with different quantum numbers and appreciable responsivity [6–8]. Among intensive research done on intersubband transitions (ISBTs) in QWs [9–13], West and Eglash [14] are the first realizing experimental measurement of the strong intersubband absorption with high oscillator strength in a series of highly doped GaAs QWs. Levine et al. [15] demonstrated the first quantum well infrared photodetector (QWIP) based on intersubband absorption between two bound QW states with large peak responsivity. And then, the intersubband absorption has been studied both theoretically and experimentally [16–22]. The asymmetry in QW structure as well as the doping of only one side [23] allow the observation of a large number of intersubband transitions which are forbidden in symmetric geometry or uniformly doped wells and increase the freedom to control the positions of the energy levels and oscillator strengths. Alves et al. [24] have fabricated a QWIP capable to sense simultaneously three different widely separate IR bands including NIR, with separate Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing 1369-8001/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mssp.2013.12.008 n Corresponding author. Tel: þ216 73500274; fax: þ216 73500278. E-mail address: samiaabdi@myway.com (S. Abdi-Ben Nasrallah). Materials Science in Semiconductor Processing 19 (2014) 83–88