Microelectronics Journal 39 (2008) 589–593 A new type of structural defects in CdZnSe/ZnSe heterostructures L. Borkovska a, , N. Korsunska a , V. Kladko a , M. Slobodyan a , O. Yefanov a , Ye. Venger a , T. Kryshtab b , Yu. Sadofyev c , I. Kazakov c a V. Lashkaryov Institute of Semiconductor Physics NASU, Pr. Nauki, 41, Kyiv 03028, Ukraine b Department of Materials Science, Instituto Politecnico Nacional-ESFM, Avenue IPN, Ed. 9 U.P.A.L.M., 07738 Mexico D. F., Mexico c Lebedev Physical Institute, RAS, Leninskii pr. 53, Moscow 117924, Russia Available online 5 September 2007 Abstract The changes of structural and photoluminescence (PL) characteristics of MBE-grown CdZnSe/ZnSe single quantum well (QW) structures caused by Cd/Zn interdiffusion were studied by high-resolution X-ray diffraction (HRXRD) and low-temperature PL methods. The PL investigations showed that the increase of Cd content in the QW resulted in the increase of the depth of potential fluctuations in the QW as well as in the decrease of ZnSe cap layer band gap (up to several meV). The HRXRD scans as well as reciprocal space maps measured for symmetrical and asymmetrical diffractions revealed the formation of CdZnSe layers near the QW/ZnSe interface with Cd content of order of several percents. It is found that in some samples, the Cd profile in these layers is rather smooth while in others it is quite abrupt. In the latter case, the partial strain relaxation can occur in these layers. r 2007 Elsevier Ltd. All rights reserved. Keywords: QW; ZnSe; CdSe; MBE; HRXRD; PL 1. Introduction An interest to II–VI heterostructures that emerged more than a decade ago was caused by their potential application in opto-electronic devices operating in visible spectral range. Among them, CdSe/ZnSe nanostructures were the most widely investigated. However, up to now the lifetime of such devices remains a major problem [1]. Investigations of degradation processes in CdZnSe quantum wells (QWs) have shown that they are accom- panied by electronically stimulated interdiffusion between barrier and well material [2]. To study Cd/Zn interdiffu- sion, a number of experiments dealing with ion implanta- tion and thermal annealing of CdZnSe/Zn(S)Se QWs and short period superlattices were done [3–6]. It has been found that Cd diffusion is governed by column II vacancies mainly [3,5]. The extreme Cd diffusion enhancement in the case of p-type ZnSe doped by N [3] was attributed to generation of the compensating defect complexes including vacancies during the growth. These defects are supposed to migrate into the QW and cause degradation. It should be noted that pronounced changes of the QW photoluminescence (PL) spectra caused by Cd/Zn inter- diffusion were observed at annealing temperatures higher than 350–400 1C [4]. As a rule, Cd diffusion in ZnSe barriers is not taken into account at typical growth temperatures (300 1C) especially if VI/II beam pressure ratio corresponds to stoichiometric growth conditions. However, early reflective high-energy electron diffraction (RHEED) and transmission electron microscopy measure- ments of CdSe/ZnSe QWs have shown that it is impossible to grow pure CdSe QWs between ZnSe barriers at temperatures above 180 1C due to intermixing of the QW and barrier material [6]. This means that interdiffusion can also influence the growth processes of CdZnSe/ZnSe QW structures. In this paper, we present the results of our investigations by low-temperature PL and high-resolution X-ray diffrac- tion (HRXRD) of Cd/Zn interdiffusion, which occurs during the growth in the CdZnSe/ZnSe single QW structures. ARTICLE IN PRESS www.elsevier.com/locate/mejo 0026-2692/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2007.07.040 Corresponding author. Tel.: +380 44 5257234; fax: +380 44 5258344. E-mail address: bork@isp.kiev.ua (L. Borkovska).