Design of GaN/AlGaN quantum wells for maximal intersubband absorption in 1.3 , l , 2 mm wavelength range V. Jovanovic  a , D. Indjin b , Z. Ikonic  b, * , V. Milanovic  a , J. Radovanovic  c a Faculty of Electrical Engineering, University of Belgrade, Bulevar Kralja Aleksandra 73, 11120 Belgrade, Yugoslavia b Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK c Institute of Physics, Pregrevica 118, 11080 Belgrade, Yugoslavia Received 6 November 2001; accepted 16 January 2002 by R. Phillips Abstract The design of rectangular GaN/AlGaN quantum wells for maximal intersubband absorption in the near infrared wavelength range 1.3±2 mm, on the 0 ! 1 electronic transition is considered, taking into account the effects of internal polarization ®elds and nonparabolicity. The nonlinear optimization method based on solving a system of nonlinear equations is employed in ®nding the structural parameters which give the maximal dipole matrix element while keeping the absorption peak at the desired wavelength. q 2002 Elsevier Science Ltd. All rights reserved. PACS: 73.20.Dx Keywords: A. Quantum wells; A. Semiconductors; D. Electron interaction 1. Introduction In the past decade a lot of fundamental and applied research has been done on the wide bandgap group-III nitride semiconductors, mainly because of their successful use as materials for laser and light emitting diodes in the blue±green and ultraviolet spectral range [1], as well as for high power and high frequency electronic devices [2]. Quite recently the intersubband transitions ISBTs) in nitride- based single or multiple quantum wells QWs) also started attracting the research attention [3±6], due to the prospect of their application in optoelectronic devices like waveguide switches, infrared photodetectors or even quantum cascade lasers. A large conduction band discontinuity DE c , 2 eV for the AlN/GaN interface) makes the QW structures based on wurtzite ternary alloys primarily AlGaN/GaN QWs) good candidates for devices in the near infrared range. In particular, the wavelengths of 1.3 and 1.55 mm, important for modern optical communications, are accessible via the ISBT in nitride QWs, and due to very short relaxation times these offer a route for achieving ultrafast optical switching necessary for Tb/s optical time division multiplexing [7±9]. The recent technological improvements in the fabrication processes using molecular beam epitaxy [10±12] encourage further research in this ®eld. QWs based on 0001)-oriented wurtzite nitride semi- conductors exhibit large intrinsic spontaneous and strain- induced piezoelectric polarization, which has a considerable impact on both the electronic and optical properties of the structure [13]. A signi®cant shortening of ISBT wavelength, as compared to the prediction of the ¯at band model [14] is found, which is thus helpful in shifting the spectral range towards the near infrared. In this paper we consider the structural parameters opti- mization of GaN/AlGaN QWs with respect to achieving maximal intersubband absorption at wavelengths ranging from 1.3 to 2 mm. The presence of the polarization ®eld makes it impossible to use the optimization techniques which rely on supersymmetric quantum mechanics [15] or inverse spectral theory [16] and in view of the current status of nitride QWs technology it would not be very helpful to have smooth grading pro®les derived by such techniques). Therefore, we consider structurally simple, rectangular QW and vary its parameters in searching for maximal Solid State Communications 121 2002) 619±624 0038-1098/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0038-109802)00036-4 PERGAMON www.elsevier.com/locate/ssc * Corresponding author. Tel.: 144-113-233-2089; fax: 144-113- 244-9451. E-mail address: z.ikonic@ee.leeds.ac.uk Z. Ikonic Â).