Fabrication of ultralow-density quantum dots by droplet etching epitaxy

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Zhiming M. Wangb) Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, People’s Republic of China

Xinlei Li MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, College of Biophotonics, South China Normal University, Guangzhou 510631, People’s Republic of China

Yuriy I. Mazur and Gregory J. Salamo Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, United States of America (Received 17 May 2017; accepted 27 September 2017)

Isolated single quantum dots (QDs) enable the investigation of quantum-optics phenomena for the application of quantum information technologies. In this work, ultralow-density InAs QDs are grown by combining droplet etching epitaxy and the conventional epitaxy growth mode. An extreme low density of QDs (;106 cm2) is realized by creating low-density self-assembled nanoholes with the high temperature droplet etching epitaxy technique and then nanohole-filling. The preferred nucleation of QDs in nanoholes has been explained by a theoretical model. Atomic force microscopy and the photoluminescence technique are used to investigate the morphological and optical properties of the QD samples. By varying In coverages, the size of InAs QDs can be controlled. Moreover, with a thin GaAs cap layer, the position of QDs remains visible on the sample surface. Such a low density and surface signature of QDs make this growth method promising for single QD investigation and single dot device fabrication. Quantum dots (QDs) are one of the most important nanostructures due to their unique properties and applications in a wide range of novel devices.1,2 Since the discovery of QDs, they have been applied to quantum devices,3 solar cells,4 lasers,5 and photodetectors.6 Fabrication of QDs with user-specified properties is desired for many different applications. For example, a high density of QDs is desired for solar cells and photodetectors, while a low density of QDs is needed in the fields of quantum computing and quantum cryptography, such as single-photon emitters.7 In the past 10 years, several approaches have been developed to obtain low densities of QDs so that each isolated single QD can be addressed optically. After InAs deposition, slightly less than the critical coverage value, postgrowth annealing is introduced to obtain low-density dots around ;109 cm2,8 ;108 cm2,9 and ;104–108 cm2.10 Also, it has been found that low densities of QDs can be obtained when InAs is intentionally deposited on the Contributing Editor: Artur Braun Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.408

sample surface inhomogeneously.11 To further reduce the QD density, the InAs coverage is intentionally varied along the surface of a highly inhomogeneous sample by stopping the rotation of the wafer during InAs deposition. After additional thermal annealing, QD density as low as 2.5  107 cm2 is achieved by using t

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