Thin film technology molecular beam epitaxy

An outgrowth of prior thin-film technology and of basic surface science research has been molecular beam epitaxy—the MBE formation... 

Thin semiconductor films (and other nanostructured materials) are widely used in many applications and, especially, in microelectronics. Current technological trends toward ultimate miniaturization of microelectronic devices require films as thin as less than 5 nm, that is, containing only several atomic layers [1]. Experimental deposition methods have been described in detail in recent reviews [2-7]. Common thin-film deposition techniques are subdivided into two main categories physical deposition and chemical deposition. Physical deposition techniques, such as evaporation, molecular beam epitaxy, or sputtering, involve no chemical surface reactions. In chemical deposition techniques, such as chemical vapor deposition (CVD) and its most important version, atomic layer deposition (ALD), chemical precursors are used to obtain chemical substances or their components deposited on the surface. 

Thin film science and technology is the deposition and characterization of layered structnres, typically less than a micron in thickness, which are tailored from the atomic scale upwards to achieve desired functional properties. Deposition is the synthesis and processing of thin films under controlled conditions of chemical processing. Chemical vapor deposition (CVD) and gas-phase molecular beam epitaxy (MBE) are two processes that allow control of the composition and structure of the films. Characterization is the instrumentation that use electrons, X-ray, and ion beams to probe the properties of the film. Epitaxial films of semiconductors are used for their electronic properties to emit light in the infrared (IR) and the ultraviolet rays. 

The preparation of well-defined thin or ultrathin crystalline films by sublimation or molecular-beam epitaxy is a technology which depends upon a large number of experimental parameters, which we cannot treat in detail here. Ultrahigh vacuum is in any case a prerequisite. More on this subject can be found for example in the review articles by Forrest [18]. 

Thin-film technology is replete with acronyms and several of the main ones you will encounter are listed in Table 28.1. Molecular beam epitaxy (MBE) is the only acronym that assumes a crystalline structure and alignment of the thin film. Molecular-beam evaporation would be much better, especially when used to grow amorphous films ... 

Recently, many scientists and engineers have looked for methods to control the sizes of QDs and make possible the formation of ordered lateral two-dimensional superlattices or vertical superlattices for heterojunction thin films. One approach is the top-down method, molecular beam epitaxy nanolithographic technology, which has been developed with the development of microelectronics and processing techniques for traditional inorganic semiconductors. This technique of nanoscale manipulation can reach only the upper limits of sizes defined by nanostructure physics, and has successfully manipulated artificial atoms and molecules [10-12). Bottom-up method is based on molecular and supramolecular assembly techniques that have been proposed by chemists in recent years. With this method, it is possible to prepare monodispersed defect-free nanocrystal QDs 1-10 nm in size and to control easily QDs coupling to form nanocrystal molecules, even quantum dot superlattices in two or three dimensions. 

S.A. Barnett, J. Poate, Molecular beam epitaxy, in D.A. Glocker, S. Ismat Shah (Eds.) Handbook of Thin Film Process Technology, vol. 1, Taylor Francis, 2002, Sec A2. 

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