Author's personal copy Structural characterization of GaSb-capped InAs/GaAs quantum dots with a GaAs intermediate layer A.M. Beltran a, ⁎, T. Ben a , A.M. Sanchez b , J.M. Ripalda c , A.G. Taboada c , S.I. Molina a a Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cádiz, Campus Río San Pedro, s/n, 11510 Puerto Real, Cádiz, Spain b Physics Department, University of Warwick, Coventry CV4 7AL, United Kingdom c Instituto de Microelectrónica de Madrid (CNM, CSIC), Isaac Newton 8, 28760 Tres Cantos, Madrid, Spain abstract article info Article history: Received 24 November 2010 Accepted 28 February 2011 Available online xxxx Keywords: Quantum dots GaAs–GaSb–InAs Transmission electron microscopy Defects GaSb incorporation to InAs/GaAs quantum dots is considered for improving the opto-electronic properties of the systems. In order to optimize these properties, the introduction of an intermediate GaAs layer is considered a good approach. In this work, we study the effect of the introduction of a GaAs intermediate layer between InAs quantum dots and a GaSb capping layer on structural and crystalline quality of these heterostructures. As the thickness of the GaAs intermediate layer increases, a reduction of defect density has been observed as well as changes of quantum dots sizes. This approach suggests a promising method to improve the incorporation of Sb to InAs heterostructures. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Nowadays, there is an intense interest in using III/V alloys for opto- electronic devices due to the importance of expanding the usable wavelength to reach 1.3–1.55 μm [1]. Although first researches were based on InAs nanostructures grown over InP, since they can emit at 1.55 μm [2], efforts are being dedicated to develop GaAs technology based-laser devices because the advantages of this technology. In this way, the growth of In(Ga)As quantum dots (QDs) over a GaAs substrate is a promising approach [3] due to their successful laser action. Moreover, the addition of Sb to these nanostructures is considered an important advance due to staggered band alignment of the GaSb/InAs [4]. It has been reported the existence of a miscibility gap for quaternary alloys of GaSb and InAs in absence of strain [5]. However, our previous studies on similar nanostructures have confirmed that due to the presence of a heterogeneous strain field in the structure, a quaternary alloy In x Ga 1-x Sb y As 1 - y is formed when a GaSb layer is directly grown over InAs/GaAs QDs [6]. The formation of this alloy affects to the opto-electronic properties [7]. These results are a tangible proof of the importance of juggling with additional components which improve the control on InAs–GaSb mixing. The aim of this work is to study the effect on the structural properties of introducing an intermediate layer of GaAs between InAs QDs and a GaSb-capped layer grown by molecular beam epitaxy (MBE). Higher QDs and an enhancement of the structural quality are observed as the thickness of the GaAs intermediate layer increases. These findings are important to design these heterostructures, in particular when they are considered in conjunction with the compositional distribution, presented in a previous work [8]. 2. Experimental Studied samples have been grown by MBE on GaAs (001) substrate. After InAs QDs growth (2.2 monolayers (ML) of InAs) at 510 °C, a GaAs intermediate layer has been deposited on the formed dots at 480 °C, followed by 3 ML of GaSb grown at 480 °C. Finally, the full heterostructure has been capped by 100 nm of GaAs at 590 °C. Three different thicknesses of GaAs intermediate layer have been analyzed: 3, 6 and 12 ML of GaAs (samples A, B and C, respectively). Structural characterization has been conducted by conventional transmission electron microscopy (CTEM) both in cross-section (X) and plan view (PV) orientations in a JEOL-JEM 1200EX operated at 120 kV and a JEOL 2011 at 200 kV. The samples have been prepared for TEM study by following standard procedures. 3. Results and discussion Dark field (DF) g002 XTEM images, whose intensity contrast is related to compositional changes in face centered cubic systems, have been acquired. In order to be able to interpret the contrasts, intensities associated to g002 reflection have been simulated following the dynamical and kinematical approaches [9] (both of them are not shown in this work). According to simulations and for areas of thickness lower than 50 nm, GaSb presents brighter contrast than InAs, In x Ga 1 - x As, GaSb y As 1 - y , but especially than GaAs and the quaternary alloy In x Ga 1-x Sb y As 1-y for an In content higher than 30%. Materials Letters 65 (2011) 1608–1610 ⁎ Corresponding author at: Present address: CEMES-CNRS 29, Rue de Jeanne Marvig, BP 94347, Toulouse 31055, France. Tel.: +34 956016335; fax: +34 956016337. E-mail address: ana.beltran@uca.es (A.M. Beltran). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.02.086 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet