Electronic structure of InAs/GaSb superlattice for the modelling of MWIR pin photodiode J. Imbert a,b,⇑ , V. Trinite a,⇑ , S. Derelle b , J. Jaeck b , E. Giard b , M. Delmas c,d , M. Carras a , R. Haidar b , J.B. Rodriguez c,d , P. Christol c,d a Thales Research and Technology, 1 Avenue Augustin Fresnel, 91767 Palaiseau, France b ONERA, Chemin de la Hunière, 91761 Palaiseau, France c Univ. Montpellier, IES, UMR 5214, F-34000 Montpellier, France d CNRS, IES, UMR 5214, F-34000 Montpellier, France highlights  We present a 18-bands k.p method to simulate energies and wavefunctions.  We study three different type of InAs/GaSb superlattices structures.  Calculated bandgaps are in good agreement with results for symmetrical superlattice.  We explain from model the difference of behaviour between the structures.  We calculate intrinsic carrier concentration and effective mass. article info Article history: Received 25 July 2014 Available online 23 October 2014 Keywords: InAs/GaSb superlattice k.p Method Modelling Carrier concentration Effective mass abstract An 18-band k.p formalism has been developed to determine the band structure and wavefunctions of InAs/GaSb type II superlattices (T2SL). Bandgap results are in good agreement with measurements for symetrical superlattices. Thus, we are able to calculate intrinsic properties of InAs/GaSb SL as the effective mass, the density of state and the free carrier concentration. Then we compare the modelled and mea- sured electro-optical properties of three different SL structures with a different InAs to GaSb thickness ratio R per SL period, but having the same cut-off wavelength of 5 lm at 77 K. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Type-2 superlattice (T2SL) is now considered as an emerging technology able to satisfy the third generation infrared imagers’ requirements [1]. Some very impressive results have been obtained the last past decade by several laboratories but, and although the T2SL is a recent technology compared to the well-established InSb, QWIP and HgCdTe technologies, the devices quite fail reaching the theoretical predicted performances. Consequently, it is necessary to develop an accurate device modelling to analyze first the phys- ical limitations of the T2SL material and devices and then to pro- pose improvements in order to overcome the current performances. The historical method for heterostructure modelling is the k.p method in the envelope function approximation [2] and this approach was employed in the well-known paper of Smith and Mailhot where T2SL structure was first proposed for infrared pho- todetector [3]. However, as we will discuss further in this paper, the use of k.p method has been questioned in the case of T2SL. Therefore other methods have been proposed. The atomistic empirical pseudo-potential (AEPM) method computes energies and wavefunctions by resolving the Bloch equation for each atom. It is an atomistic method quite complicates to implement with a high number of adjustable parameters, but very precise in its description of the structure especially for the interface [4]. Dente and Milton [5] proposed an easier version of AEPM adapted for superlattices, the superlattice empirical pseudopotential (SEPM). This method has less parameters and mostly less adjustable parameter and is easier to implement for equivalent results. Another method is the empirical tight-binding method, where a http://dx.doi.org/10.1016/j.infrared.2014.09.035 1350-4495/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding authors at: Thales Research and Technology, 1 Avenue Augustin Fresnel, 91767 Palaiseau, France (J. Imbert). Tel.: +33 169 415 682. E-mail addresses: julien.imbert@onera.fr (J. Imbert), virginie.trinite@3-5lab.fr (V. Trinite). Infrared Physics & Technology 70 (2015) 81–86 Contents lists available at ScienceDirect Infrared Physics & Technology journal homepage: www.elsevier.com/locate/infrared