Vapor-phase molecular layer 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. 

In the new method for organic multilayers deposition, molecular layer epitaxy (MLE), the epitaxial growth is achieved by self-limited vapor-phase reactions on a templated surface. As in ALE method, MLE is governed by covalent bonding at the intermolecular level that leads to ideal monomolecular growth. The chemical principles of the MLE method can be divided into four levels (i) a template layer, (ii) self-restricted vapor phase reactions, (Hi) covalent ( c-axis ) interlayer bonding and (iv) 7C-stacking in x-y plane. 

R. J. Molmr, Hydride Vapor Phase Epitaxial Growth of TTI-V Nitrides T. D. Moustakas, Growth of III-V Nitrides by Molecular Beam Epitaxy Z. Liliental-Weber, Defects in Bulk GaN and Homoepitaxial Layers C G. Van tie Walk and N. M. Johnson, Hydrogen in III-V Nitrides... 

Fig. 8. Energy below the conduction band of levels reported in the literature for GaAs. Arrangement and notations are the same as for Figs. 4 and 5. Notations not defined there are epitaxial layer on semi-insulating substrate (EPI/SI), boat-grown (BG), vapor phase epitaxial layer on semi-insulating substrate (VPE/SI), melt-grown (M), molecular beam epitaxy (MBE), horizontal Bridgman (HB), irradiated with 1-MeV electrons or rays (1-MeV e, y), thermally stimulated capacitance (TSCAP), photoluminescence excitation (PLE), and deep level optical spectroscopy (DLOS).

Epitaxial Layers. Epitaxial deposition produces a single crystal layer on a substrate for device fabrication or a layer for multilevel conductive interconnects which may be of much higher quality than the substrate. The epitaxial layer may have a different dopant concentration as a result of introducing the dopant during the epitaxial growth process or may have a different composition than the substrate as in silicon on sapphire. Methods used for epitaxial growth include chemical vapor deposition (CVD), vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE) and solid phase epitaxy (SPE). 

Physical vapor deposition and chemical vapor deposition are both techniques for producing thin films. Both rely on the transfer of mass from the vapor phase to a solid surface. A third technique, related to chemical vapor deposition but generally considered distinct from it, is molecular beam epitaxy (MBE) (Joyce and Joyce, 2004), in which a neutral beam of atoms is used to deposit a layer of adsorbed atoms. To deposit a compound, two molecular beams are used, depositing the constituent elements in the compound sequentially. Although this appears to make the deposition of any size film of any composition a simple matter (shown schematically below in Figure 3.26), the technical requirements for achieving this deposition are severe. 

The methods available for preparation of the different layers in thin-film solar cells include physical methods such as vacuum sputtering, vapor-phase deposition, and molecular beam epitaxy as well as chemical methods such as chemical vapor-phase deposition, metal organic vapor-phase epitaxy, chemical bath deposition (CBD), and electrochemical deposition (ED). This chapter explores the potential of electrodeposition as a route to the fabrication of absorber layers such as CdTe, CIGS, and CZTS for thin-film solar cells. Electrochemistry may also be usefiil for the preparation of transparent layers such as ZnO this topic has been reviewed by Pauporte and lincot [13]. 

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. 

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