Langevin approach to the generation–recombination noise of a multi quantum well infrared photodetector A. Carbone a, * , R. Introzzi b ,H.C.Liu b a Dipartimento di Fisica and INFM, Politecnico di Torino, Corso Duca degli Abruzzi 24, I-10129 Torino, Italy b Institute for Microstructural Sciences, National Research Council, Ottawa, Ontario, Canada K1A 0R6 Available online 13 April 2005 Abstract The current noise power spectrum of a multi quantum well infrared photodetector is calculated using a Langevin- transport equation where a discrete distribution of the electric field in the quantum well region, rather than the homogeneous one valid for bulk semiconductors, has been considered. The discreteness of the electric field arises as aconsequenceofthediscretestructureofthequantumwelllayers.Theinhomogeneouschargedistributioninthequan- tumwellstructureaffectstheintensityandthefrequencydependenceofthenoisepowerspectrum,givingrisetodevi- ationsfromthebehaviorexpectedonthebasisofasimplemodelbasedonfullyuncorrelatedfluctuationprocesses.The modelreproducesthedifferent N-dependenceofthecurrentnoisepowerspectraldensityinthedarkandinthepresence of radiation. In particular, its relation to the discrete structure of the device arises as a consequence of the imbalance betweenthecurrentinjectedattheemitterandthestreamofphotoelectronsdriftingthroughthestructure,whoseeffect seems particularly relevant for small values of the number of quantum wells N. Ó 2005 Published by Elsevier B.V. PACS: 73.40.c; 72.70.+m; 05.40.a Keywords: Dark noise; Photocurrent noise; Quantum well infrared photodetectors 1. Introduction Quantum Well Infrared Photodetectors (QWIPs) based on the intersubband transitions in GaAs/AlGaAs have been developed over the past decade mainly to overcome the limits of the bulkIRsemiconductortechnologies [1,2].Todate, the QWIP can be considered the ideal candidate for the manufacturing of large-area focal plane array thanks to the higher detectivity, uniformity, stability, narrow band responsivity and flexible wavelength-tailorability compared to the standard 1350-4495/$ - see front matter Ó 2005 Published by Elsevier B.V. doi:10.1016/j.infrared.2005.02.005 * Correspondingauthor.Tel.:+390115647378;fax:+39011 564 7399. E-mail address: anna.carbone@polito.it (A. Carbone). Infrared Physics & Technology 47 (2005) 9–14 www.elsevier.com/locate/infrared