Istituto dei materiali per l'elettronica ed il magnetismo     
Seravalli L., Trevisi G., Frigeri P., Franchi S., Bocchi C. Low Density Metamorphic Quantum Dot structures with emission in the 1.3 - 1.55 Ám window. In: QD2010 - Quantum Dot 2010 (Nottingham, UK, 26-30 April 2010).
Emission of single photons in the 1.3 - 1.55 Ám optoelectronic window is a topic of great technological interest for growing fields such as quantum cryptography and quantum computation; InAs self-assembled quantum dots (QDs) are viable candidates to develop single photon sources due to: i) easy integration in standard optoelectronic device structures, ii) possible tuning of QD emission in the windows of interest, and iii) growth of structures on GaAs substrates, with advantages over the InP option. While good results have been obtained in redshifting light emission up and beyond 1.55 Ám from high density QD structures, emissions beyond 1.3 Ám from low density QDs have been reported much more rarely [1-3]. In order to tune the emission of InAs QDs in the whole 1.3 - 1.6 Ám range, we use the Quantum Dot Strain Engineering (QDSE) approach, where QDs are deposited on InGaAs metamorphic buffers that act as confining layers (CLs). Thanks to the reduction of the QD strain, the QD emission wavelength can be shifted up to 1.59 Ám at RT [4,5]. To achieve low densities we considered the deposition of InAs coverages below the critical thickness for dot nucleation followed by a growth interruption, method that has been used so far only on GaAs [6,7]. We grew by MBE and characterized by PL and AFM quantum dot structures grown on InxGa1-xAs (x = 0.15, 0.30) metamorphic buffers with subcritical coverage and growth interruptions that allow the achievement of 108 cm-2 QD density. We studied the deposition of subcritical coverages on the InGaAs buffers and evidenced the differences with the deposition on GaAs due to the different lattice parameter and composition of the overgrown layer. By carefully adjusting the coverage value and the growth interruption time we were able to obtain QD densities of 5 x 108 cm-2. While by using In0.15Ga0.85As buffers emission at 10K was limited to 1.2 Ám, structures grown on In0.30Ga0.70As buffers show emission peaked at 1.3 Ám. Furthermore, in the x = 0.30 structures, the change in composition of the InyGa1-yAs (y = 0.30, 0.40, 0.50, 0.60) upper confining layers (UCLs) allowed to redshift even further the QD emission, up to a value of 1.64 Ám at 10K, at the cost of a reduction of the light intensity as compared with structures with x = y. This result could allow the development of GaAs-based quantum dot structures for single photon sources with emission in the optoelectronic window of fiber-based telecommunication. References [1] Trevisi G, Seravalli L, Frigeri P and Franchi S. 2009 Nanotechnology 20 415607 [2] Alloing B, Zinoni C, Li LH, Fiore A and Patriarche G 2007 J. Appl. Phys. 101 024918 [3] Semenova E, Hostein R, Patriarche G, Mauguin O, Largeau L, Robert-Philip I, Beveratos A and Lemaıtre A 2008 J. Appl. Phys. 103 103533 [4] Seravalli L, Frigeri P, Trevisi G, Franchi S 2008 Appl. Phys. Lett. 92 213104 [5] Seravalli L, Minelli M, Frigeri P, Franchi S, Guizzetti G, Patrini M, Ciabattoni T, Geddo M 2007 J. Appl. Phys. 101 024313 [6] Song H Z, Usuki T, Nakata Y, Yokoyama N, Sasakura H and Muto S 2006 Phys. Rev. B 73 115327 [7] Li LH, Chauvin N, Patriarche G, Alloing B, Fiore A 2008 J. Appl. Phys. 104 083508.
Subject InAs/GaAs Quantum Dots

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