IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 22 (2011) 055706 (5pp) doi:10.1088/0957-4484/22/5/055706 Lateral interdot carrier transfer in an InAs quantum dot cluster grown on a pyramidal GaAs surface B L Liang 1 , P S Wong 2 , N Pavarelli 3,4 , J Tatebayashi 2 , T J Ochalski 3,4 , G Huyet 3,4 and D L Huffaker 1,2 1 California Nanosystems Institute, University of California at Los Angeles, Los Angeles, CA 90095, USA 2 Electrical Engineering Department, University of California at Los Angeles, Los Angeles, CA 90095, USA 3 Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland 4 Center for Advanced Photonics and Process Analysis, Cork Institute of Technology, Cork, Ireland Received 24 July 2010, in final form 15 October 2010 Published 22 December 2010 Online at stacks.iop.org/Nano/22/055706 Abstract InAs quantum dot clusters (QDCs), which consist of three closely spaced QDs, are formed on nano-facets of GaAs pyramidal structures by selective-area growth using metal–organic chemical vapor deposition. Photoluminescence (PL) and time-resolved PL (TRPL) experiments, measured in the PL linewidth, peak energy and QD emission dynamics indicate lateral carrier transfer within QDCs with an interdot carrier tunneling time of 910 ps under low excitation conditions. This study demonstrates the controlled formation of laterally coupled QDCs, providing a new approach to fabricate patterned QD molecules for optical computing applications. 1. Introduction A semiconductor quantum dot (QD) is an atom-like structure with three-dimensional (3D) quantum confinement, which gives rise to the complete localization of carriers and a discrete energy spectrum with a δ-like density of states [1, 2]. These characteristics lead to QDs with unique optical and electronic properties useful for the development of opto-electronic devices [3–5]. An interesting example is represented by groups of closely spaced QDs, called QD molecules (QDMs), since they are anticipated as a platform for studying interacting electronic systems and performing complex quantum computing [6, 7]. A well-developed technique to fabricate such QDMs is the epitaxial growth of vertically aligned QDs [8–10], where the vertical coupling between QDs can be tuned either by a spacer between QD layers or by an external electrical field. Another approach is to fabricate laterally coupled QDMs where the laterally coupled configuration can offer more flexibility for the fabrication and operation of QDM devices [11]. However, the stochastic nature of self-assembly growth of QDs generally results in a random distribution of QD size and location, which presents an obstacle for the formation of lateral QDMs. In order to remedy this issue, many attempts at forming laterally grouped QDMs or QD-clusters (QDCs) have been studied using strain engineering or selective-area epitaxy [11–16], although only a few of them have been verified to exhibit lateral interdot coupling. Recently our group has explored the nucleation of patterned InAs QDs on nano-faceted GaAs pyramids, and the nano-faceted GaAs pyramid can provide a controllable nucleation platform for the formation of a group of closely spaced QDCs [17–19]. In this work, we investigate the optical properties of these InAs QDCs by photoluminescence (PL) and time-resolved PL (TRPL) measurements. Interdot coupling and lateral energy transfer within the QDCs are demonstrated, thus indicating their potential to perform complex quantum entanglement and computing operations. 2. Experiments The sample growth is carried out using a low-pressure (60 Torr) vertical Thomas Swan metal–organic chemical vapor deposition (MOCVD) reactor with trimethylgallium, trimethylindium, and tertiarybutylarsine on a GaAs(100) substrate masked with a patterned SiO 2 mask (25 nm thick). 0957-4484/11/055706+05$33.00 © 2011 IOP Publishing Ltd Printed in the UK & the USA 1