Gas phase molecular beam epitaxy

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. 

Usually, one speaks of epitaxial growth in cases where the stmcture of a film grown from the gas phase is essentially determined by the structure of the substrate. Epitaxy in the precise sense means that the crystal structure of the substrate is continued within the growing fUm. This is possible when the crystal stractures of the substrate and the growing film are commensurate. Examples are shown in Eigs. 1.9 and 2.23. Frequently, one refers also to Organic Molecular-Beam Epitaxy, OMBE. 

Smdies on techniques for thin film deposition divide these into two groups, depending on the nature of the deposition process. Physical methods include physical vapor deposition (PVD), laser ablation, molecular beam epitaxy and sputtering. Chemical methods comprise of gas phase and solution deposition. The gas phase techniques include chanical vapor deposition (CVD) and atomic layer epitaxy (ALE). Spray-pyrolysis deposition, sol-gel, spin-coating and dip-coating are techniques based on solution deposition. 

An intriguing example for bond-creating chemical reconstructions is the GaAs(lOO) surface. Also, in this orientation, the surface is composed of alternating layers of Ga and As, and thus the surface stoichiometry depends on the actual termination even in bulk truncation, similar to the cases of ordered alloys. Surface phases with varying chemical termination can be prepared by changing the parameters in molecular beam epitaxy [118]. Different from the case of Si(lOO),... 

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