Order and disorder in the heteroepitaxy of semiconductor nanostructures

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• 作者：Fulvio Ratto ; Federico Rosei
• 关键词：Semiconductor heteroepitaxy ; Epitaxial nanostructures ; Self-organization ; Self-ordering ; Substrate patterning ; Lithography
• 刊名：Materials Science and Engineering: R: Reports
• 出版年：2010
• 出版时间：22 November 2010
• 年：2010
• 卷：70
• 期：3-6
• 页码：243-264
• 全文大小：1522 K

文摘

The heteroepitaxy of semiconductor pairs with a small lattice mismatch is a process of tremendous interest in materials science and technology. The principal mechanism of strain relief in these interfaces is the formation of three dimensional islands either directly on a bare substrate (Volmer–Weber growth mode) or following the formation of an initially flat wetting layer (Stranski–Krastanov growth mode). The elemental and strain inhomogeneities associated with these three dimensional islands may result into a confinement potential for electrons and/or holes, as in a standard quantum well. At variance with a standard quantum well, the confinement in these nanostructures (often referred to as ‘quantum dots’ (QDs)) occurs in all three spatial dimensions and over length scales comparable with the relevant De Broglie wavelength. This strong confinement may give rise to a discrete spectrum of charge carrier energy levels, as in an artificial atom. On the other hand the spectra of these nanostructures may be tuned with their physical and chemical properties, providing an enabling opportunity to design novel optical and electronic components. Epitaxial nanostructures are proposed as the building blocks of a variety of innovative applications, which may represent step-change solutions to many challenges in the fields of photonics and electronics, such as e.g. new possibilities to integrate versatile lasers and transistors in Information and Communication Technologies and to replace MOSFET devices with miniature components capable of sustaining the race to miniaturization of integrated circuits. Examples of possible applications include lasers, optical detectors, white-light sources, single-photon and entangled-pair sources, single electron transistors, quantum cellular automata, quantum bits, etc.

To harness these properties and bring these functionalities to fruition, the ability to manufacture individual QDs may be not enough. Rather, the next critical issue is to gain control over the location of nanostructures with respect to each other and their surroundings, both on a surface and in a three dimensional architecture. The exploration of this issue is essential to engineer nanostructure density, mutual interactions (hybridization of electron energy levels, charge interactions, spin interactions, etc.) and the interface with the external circuitry (electrodes, gates, wires, etc.). Moreover in some applications the principal feature is the layout of a huge number of QDs with respect to each other's nearest neighbours (as e.g. in a laser), whereas in other applications it is the precise location of a possibly smaller number of QDs within a complex architecture (as e.g. in an SET or QCA platform).

An ample variety of natural (bottom–up, parallel) and artificial (typically integrated top–down and bottom–up, sequential and/or parallel) methods have been reported to yield some extent of control over nanostructure positioning. This review aims at highlighting some of the most relevant concepts developed over recent years. While a significant number of reviews on different aspects of the synthesis and characterization of individual nanostructures are found in the literature, the complexity of the issues mentioned above has never been addressed within a dedicated framework so far.