Isotropic Lateral Ordering of III-V Quantum Dots Over GaAs (001) By Self-Assembly
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Isotropic Lateral Ordering of III-V Quantum Dots Over GaAs (001) By Self-Assembly Mohammad L. Hussein, Euclydes Marega, and Gregory Salamo Microelectronics-Photonics, University of Arkansas, Fayetteville, AR, 72701 ABSTRACT Lateral ordering of InGaAs quantum dots over GaAs (001) has been achieved in earlier reports resembling anisotropic pattern. We present in this letter a method of breaking the anisotropy of ordered QDs by changing the growth environment. We do show experimentally that using As2 molecules instead of As4 as a background flux is effective in controlling the diffusion of Ga adatoms in away to make it possible to produce isotropic ordering of InGaAs QDs over GaAs (001). Our results are consistent with reported experimental and theoretical studies on surface structure and diffusion mechanism over GaAs.
INTRODUCTION Self-assembled quantum dots (QDs) have been investigated and proposed as a promising candidate for a new generation of lasers, detectors and photonic crystals [1]. However, many applications require uniformity in size and shape and control of the spatial distribution of the QDs in order to realize their potential advantages [1,2]. For example, application of InGaAs QDs grown on GaAs (001) has been limited due to the random nucleation of the self-assembly process [3]. While recent approaches using lithographic techniques have demonstrated successful lateral ordering of QDs [4-6], these methods require expensive processing steps which are also at risk to the introduction of defects that can also prevent successful application. In an effort to overcome some of these difficulties lateral and vertical ordering of InGaAs QDs on a GaAs (001) surface have been recently investigated utilizing the technique of selforganization through vertical stacking of QDs with growth at relatively high temperatures [7]. For example, ìchainsî of ordered QDs have been fabricated using this approach and is explained in terms of preferred adatom diffusion and strain relaxation along the [1-10] direction [8-10]. The chain-like lateral ordering is characterized by QDs that are very close to each other along the chain direction. In addition to vertically ordered QD chains there has also been an effort to achieve 2D lateral ordering along with vertical ordering in order to fabricate 3D QD arrays. For example, while 2D lateral ordering on a GaAs (001) surface has been difficult to achieve due to the anisotropy of that surface [11], high index substrates have been used to engineer a uniform surface diffusion profile to achieve vertically ordered planes of 2D laterally ordered QDs [12]. While this approach has been very successful, for some applications, one can expect a preference for lateral ordering on (001) substrates. In this letter, we report on the observation of vertically ordered planes of 2D laterally ordered QDs with low indium composition (less than 40%) on a GaAs (001) surface. This was accomplished by using As2 molecules as opposed to As4 molecules as a background environment. Using As2 molecules
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