Ordering of InGaAs Quantum Dots Grown by Molecular Beam Epitaxy under As 2 gas flux
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Ordering of InGaAs Quantum Dots Grown by Molecular Beam Epitaxy under As2 gas flux Mourad Benamara1,*, Yuriy I. Mazur1, Peter Lytvyn1,2, Morgan E. Ware1, Vitaliy Dorogan1, Xian Hu1, Leonardo D. de Souza1,3, Euclydes Marega3, Marcio Theodores3, Gilmar Marques3 and Greg Salamo1 1
Institute for Nanoscience & Engineering, University of Arkansas, Fayetteville AR 72701, USA. V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, Kiev 03028, Ukraine. 3 Dept de Física, Universidade Federal de São Carlos, 13.565-905, São Carlos, São Paulo, Brazil. * E-mail address: [email protected] 2
ABSTRACT The influence of the substrate temperature on the morphology and ordering of InGaAs quantum dots (QD), grown on GaAs (001) wafers by Molecular Beam Epitaxy (MBE) under As2 flux has been studied using Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Photoluminescence (PL) measurements. The experimental results show that lateral and vertical orderings occur for temperatures greater than 520°C and that QDs self-organize in a 6fold symmetry network on (001) surface for T=555°C. Vertical orderings of asymmetric QDs, along directions a few degrees off [001], are observed on a large scale and their formation is discussed. INTRODUCTION Optoelectronic devices have long benefited from the improvement of crystal growth techniques aimed at obtaining nanoscale InGaAs quantum dots (QD) with discrete electronic spectrum [1]. In order to enhance device performance, ordered arrays of QDs with uniform size and shape are ultimately desired. The uniformity of the lateral and vertical QD alignments in multilayer structures has been established both theoretically and experimentally to depend on the degree of crystal anisotropy, the mechanical inter-layer coupling governed by the thickness of the spacer layers, or the crystallographic orientation of the growth surface [2]. In this paper, we propose to study the effect of the growth temperature on the spatial ordering of QDs grown by Molecular Beam Epitaxy with an As2 flux. EXPERIMENT QD superlattices were grown by Molecular Beam Epitaxy (MBE) on semi-insulating GaAs (001) substrates using an As2 flux. First, the native oxide layer was removed from the substrate and a 300 nm GaAs buffer was grown at 580°C. The temperature was then reduced to the superlattice growth values for each sample and a 15 period multilayer structure was grown.
Each period consists of the deposition of 9 monolayers (MLs) of In0.4Ga0.6As followed by 60ML GaAs spacers. The superlattice growth temperatures were 510°C, 520°C, 530°C, 540°C and 555°C. Details about the growth procedure have been published elsewhere [3]. For each sample, the superlattice structure was terminated with an uncapped layer of InGaAs QDs. Atomic force microscopy (AFM) was then used to characterize the morphology of the QDs with the assumption that after the first few QD layers, subsequent layers are similar. The AFM images on these uncapped QDs, were obtained using a NanoScope IIIa Dimension 3000 TM scanning probe microscope op
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