Optical properties of InGaAs QDs grown in a GaAs matrix by MOCVD, emitting at 1300 nm at room temperature
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Optical properties of InGaAs QDs grown in a GaAs matrix by MOCVD, emitting at 1300 nm at room temperature M. T. Todaro, M. De Giorgi, V. Tasco, M. DeVittorio, A. Passaseo and R. Cingolani National Nanotechnology Laboratory of INFM (NNL-INFM), Dipartimento di Ingegneria dell’ Innovazione, Università di Lecce, Via Arnesano, 73100 Lecce (ITALY). E-mail:[email protected] ABSTRACT We investigate the optical properties of InGaAs QDs emitting at 1330 nm, directly grown by Metal Organic Chemical Vapor Deposition (MOCVD) in a GaAs matrix, without indium in the barrier. The PL characterization of this new kind of QDs, shows very narrow lineshape at room temperature and a strong reduction of the temperature dependent quenching of the emission (a factor of 3 from 30 K to 300 K). The quantum external efficiency obtained by inserting such QDs into light emitting diode structures, despite the low dot density (1.6*109 cm-2), is 0.03%. This value corresponds to an individual QD efficiency about 30% higher than that reported in the literature for state of art InGaAs/InGaAs QD LEDs. INTRODUCTION Self-assembled In(Ga)As/GaAs quantum dots (QDs) have attracted considerable interest for the investigation of new physics as well as for their application to high performance light emitting devices such as single photon sources [1], light emitting diodes [2] and lasers [3]. Progress in the growth of self-assembled In(Ga)As QDs on GaAs substrates has permitted the emission wavelength to be extended to around 1300 nm, one of the low absorption wavelengths for optical fiber communications. The most effective approach to achieve 1300 nm emission by both molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) growth techniques was to embed QDs into a barrier of InxGa1-xAs ternary compound [4,5,6]. We found a new method to tune the wavelength emission above 1300 nm by MOCVDgrowth, embedding InGaAs QDs directly into a binary GaAs matrix [7]. The lack of indium in the barrier offers several advantages, namely reduced strain and reduced In intermixing, and improves the electronic properties such as the carrier confinement in the QD. This allows the fabrication of structures operating at 1300 nm, useful both for laser applications, where high gain active materials can be obtained by stacking several QD layers, and for single photon emitters, in which one or a few dots must be isolated. In this work, we investigate the optical properties of this new type of InGaAs QDs, grown directly into a binary GaAs matrix and emitting at 1330 nm at room temperature. From PL measurements at different temperatures we find optimal properties of our QDs in terms of narrowing of lineshape and strong reduction of the temperature dependent quenching of emission. Moreover, inserted in diode structures, these nanostructures show a quantum efficiency per dot, which is the highest value reported in the literature.
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EXPERIMENTAL DETAILS The structures studied in this work were grown on (100) semi-insulating (SI) GaAs substrates
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