Comprehensive investigation of optical and electronic properties of tunable InAs QDs optically active at O-band telecommunication window with (In)GaAs surrounding material O. Nasr a , M.H. Hadj Alouane a,n , H. Maaref a , F. Hassen a , L. Sfaxi a , B. Ilahi a,b a Université de Monastir, Laboratoire de Micro-Optoélectronique et Nanostructures, Faculté des Sciences, Avenue de l'environnement, 5019 Monastir, Tunisia b Department of Physics & Astronomy, College of Sciences, King Saud University,11451 Riyadh, Saudi Arabia article info Article history: Received 22 December 2012 Received in revised form 30 October 2013 Accepted 4 December 2013 Available online 12 December 2013 Keywords: Quantum dots InGaAs strain reducing layer Photoluminescence Photoreflectance abstract In this paper, we report on the impact of InAs quantum dots' (QDs) position within InGaAs strain reducing layer on their structural and optical properties. Morphological investigation revealed that the QD' size and density are strongly dependent on the InGaAs underlying layer's thickness. Additionally, comprehensive spectroscopic study by room temperature photoreflectance spectroscopy (PR) and temperature dependent photoluminescence (PL) showed that indium segregation and strain driven alloy phase separation alter both the QDs and their surrounding materials. Embedding or covering the InAs QDs by InGaAs has been found to improve their overall properties including an extended emission wavelength up to 1.3 μm. However a pronounced degradation has been observed when growing them on the top of the strain reducing layer, resulting in a broadened size distribution and atypical temperature dependent emission energy and linewidth. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Self assembled quantum dots (QDs), formed by Stranski–Krastanow (SK) growth mode, with three dimensional quantum confinements have attracted great attention in the past decades due to their atomic-likes properties. This makes them suitable in widely poten- tial applications such as solar cells [1], micro-cavity light-emitting- diodes [2], infrared photodetectors [3] and lasers [4,5]. The studies of various QDs' structure has been conducted in a wide range of high performance optoelectronic devices and the identification of unique physical phenomena such as lower threshold current density, ultrahigh characteristic temperature and high differential gain [6,7]. In particular, the incorporation of InAs/GaAs QDs as the active medium open new perspectives of obtaining QDs' light emission in the International Telecommunication Union (ITU) O-band (1.26–1.36 mm) window operating at room temperature [8]. Accordingly, several groups have reported that the performance of the QDs' light emission can be improved significantly by either using InGaAs strain reducing underlying layer (SRUL) [9,10] or strain reducing capping layer (SRCL) [11–13]. Combining the two approaches, advanced quantum dot-in-a-well (DWELL) structure can be configured and offer better performance devices [14,15]. Furthermore, replacing the GaAs capping layers by InGaAs layers leads to partial strain relief-induced modification of confinement potential allowing to manipulate inter and intraband transitions in InAs QDs. It has been demonstrated that changing the compositions of barriers leading to a modification in the physical properties of QDs. These works mainly investigated the different approaches separately and are usually focused on the transitions in QDs whereas less attention has been devoted to the characteristics of quantum well (QW) barriers. However, the properties of InGaAs surrounding material are crucial for the design of optoelectronic devices operat- ing at room temperature. This becomes more complicated because discrete levels in the zero-dimensional QDs are combined in the two-dimensional InGaAs QW. In that case, the QW is usually optically inactive in emission type of experiment since the majority of radiative recombination goes through the QDs states. In this work, we systematically study the optical properties of both QD and QW transitions in quantum dot strain engineered InAs/ (In)GaAs nanostructures designed for room temperature emission in the ITU O-band. By combining photoluminescence (PL) and photo- reflectance spectroscopy (PR), detailed understanding of the critical energy states is investigated. An atomic force microscope (AFM) images are used to confirm the optical results. The aim of these experiments is to identify the carrier escape process; in particular the final states of the thermal transitions which are highly attractive for future QDs based optoelectronic components. 2. Experiments The samples under investigation consist of a single InAs QDs layer grown by molecular beam epitaxy on Si-doped (0 0 1) GaAs Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2013.12.004 n Corresponding author. Tel.: þ21622720305. E-mail address: helmi.alouane@yahoo.fr (M.H. Hadj Alouane). Journal of Luminescence 148 (2014) 243–248