Site-controlled In(Ga)As/GaAs quantum dots for integration into optically and electrically operated devices A. Huggenberger n , C. Schneider, C. Drescher, S. Heckelmann, T. Heindel, S Reitzenstein, M. Kamp, S. H¨ ofling, L. Worschech, A. Forchel Technische Physik and Wilhelm Conrad R¨ ontgen-Center for Complex Material Systems, University W¨ urzburg, Am Hubland, D-97074 W¨ urzburg, Germany article info Available online 2 December 2010 Keywords: A1. Nanostructures A3. Quantum dots A2. Site-controlled growth B2. Semiconducting III–V materials abstract We investigated the growth and device integration of site-controlled In(Ga)As quantum dots (SCQDs) on a pre-patterned substrate. A high substrate temperature of 545 1C during growth ensures optimal SCQD nucleation on square arrays from 200 nm up to 10 mm period. The SCQDs exhibit a small inhomogeneous broadening of the ensemble emission and a rather narrow single SCQD linewidth. We used a scalable alignment technique to integrate the SCQDs into a p–i–n diode and observe electroluminescence of a single SCQD with a linewidth of 400 meV. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Site-controlled quantum dots (SCQDs) attract great interest since they allow for the scalable fabrication of many semiconductor devices like for instance, single photon sources [1]. Also the scalable realization of ultra-small lasers with only one SCQD in the laser cavity [2,3] is only feasible by combining the growth of SCQDs with an excellent alignment technique. The integration of SCQDs in electrically addressable micropillar structures could potentially facilitate the scalable fabrication of triggered, highly efficient single photon sources [4]. So far the optical quality of In(Ga)As SCQDs grown by molecular beam epitaxy (MBE) on pre-patterned (1 0 0)- GaAs substrates is severely reduced by the effects of spectral diffusion [5,6]. During the pre-patterning of the substrate, crystal defects are created on the etched surface. When excited above the GaAs band gap the emission from SCQDs is influenced by the Coulomb interactions from charge carriers that are trapped at and released from these defects on a time-scale much faster than the integration time of the luminescence signal from the SCQD [7]. This effect broadens the linewidth of the single SCQD emission and hinders the observation of cavity quantum electrodynamical (cQED) effects like e.g. strong coupling of a SCQD to the cavity mode of a microresonator. Here, we study a growth method to attenuate the effects of spectral diffusion and reduce the single SCQD linewidth using an advanced growth scheme that increases the distance of the SCQDs from the etched surface but preserves the position control. We also show that these optimized SCQDs can be integrated into an optically driven single photon source and into a p–i–n diode that shows single quantum dot electroluminescence. 2. Growth of site-controlled quantum dots The samples are grown on (1 0 0)-oriented GaAs substrates by solid source MBE. To investigate the SCQD nucleation we used a 400 nm-thick GaAs buffer layer on an undoped substrate that was pre-patterned by a combination of optical and e-beam lithography. Details about this process are published elsewhere [6,8]. After the fabrication the samples are heated up to 400 1C for 1 h in the load lock chamber of the MBE system to remove contaminations. This is followed by an atomic hydrogen cleaning step for 30 min at a substrate temperature of 360 1C and a hydrogen pressure of 3.0  10 5 Torr that removes the surface oxide [9]. After transfer- ring the sample into the growth chamber, the nano-holes are overgrown by an 8 nm-thick GaAs layer that smoothens surface roughness. Then, InAs at a growth rate of 0.005–0.010 nm/s is provided at a substrate temperature of 545 1C. This high substrate temperature enhances both the migration length of the indium adatoms on the surface and desorption of indium. Therefore the actual growth rate is reduced and only a small amount of InAs sticks to the surface—preferentially accumulating in the nano-holes. The amount of InAs in this layer is not enough to form quantum dots (QD) that can be observed with an electron microscope, but a partly filling of the nano-holes occurs (see Ref. [8] for a SEM micrograph). We could not find any emission from this layer in reference samples. Therefore we consider this layer to be optically inactive. This so-called seeding layer is overgrown by a 10 nm separation layer consisting of 5/3/2 nm GaAs/Al 0.33 Ga 0.67 As/GaAs. InAs is deposited for 160 s on the separation layer and it preferentially Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.11.144 n Corresponding author. Tel.: + 49 931 31 86287; fax: + 49 931 31 85143. E-mail address: alexander.huggenberger@physik.uni-wuerzburg.de (A. Huggenberger). Journal of Crystal Growth 323 (2011) 194–197