MBE—See Molecular beam epitaxy

Silicon Epitaxy. A critical step ia IC fabricatioa is the epitaxial depositioa of sdicoa oa an iategrated circuit. Epitaxy is defined as a process whereby a thin crystalline film is grown on a crystalline substrate. Silicon epitaxy is used ia bipolar ICs to create a high resistivity layer oa a low resistivity substrate. Most epitaxial depositioas are doae either by chemical vapor depositioa (CVD) or by molecular beam epitaxy (MBE) (see Thin films). CVD is the mainstream process. 

Epitaxial crystal growth methods such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have advanced to the point that active regions of essentially arbitrary thicknesses can be prepared (see Thin films, film deposition techniques). Most semiconductors used for lasers are cubic crystals where the lattice constant, the dimension of the cube, is equal to two atomic plane distances. When the thickness of this layer is reduced to dimensions on the order of 0.01 )J.m, between 20 and 30 atomic plane distances, quantum mechanics is needed for an accurate description of the confined carrier energies (11). Such layers are called quantum wells and the lasers containing such layers in their active regions are known as quantum well lasers (12). 

Fig. 4. Schematic of an ultrahigh vacuum molecular beam epitaxy (MBE) growth chamber, showing the source ovens from which the Group 111—V elements are evaporated the shutters corresponding to the required elements, such as that ia front of Source 1, which control the composition of the grown layer an electron gun which produces a beam for reflection high energy electron diffraction (rheed) and monitors the crystal stmcture of the growing layer and the substrate holder which rotates to provide more uniformity ia the deposited film. After Ref. 14, see text.

Clearly, there are situations where we have to give up this assumption. A typical case is molecular beam epitaxy (MBE) (see [3,12-14] and [15-19]), where particles are shot onto the surface of a crystal rather than condensing slowly from a thermally equilibrated vapor-phase. In this case we will have to be very specific about all the experimental boundary conditions and... 

The impetus for this topic has been provided by the development of molecular beam epitaxy (MBE) as a viable thin film deposition process [ 111]. As a result, the approach has concentrated more on investigations of reaction kinetics than on electronic effects, since kinetic parameters are directly available from modulated molecular beam measurements (see Sect. 2.4.1). We will summarize here only the results for beams of As4 and As2 interacting with 100 GaAs surfaces, but closely similar behaviour is observed for other Group V elements and other Group III—V compound surfaces. The choice of tetramer and dimer beams is dictated by the evaporation behaviour of Group V elements in that elemental sources produce tetramers and Group III—V compound sources produce dimers. Monomeric species are not readily available. 

For details of MBE growth, see Herman, M.A. and Sitter, H., (1996) Molecular Beam Epitaxy Fundamentals and Current Status, 2nd edn, Springer, Berlin. 

Molecular beam epitaxy (MBE) The epitaxial growth of a single-crystal film produced in a very good vacuum using a well-controlled beam of atomic or molecular species that is usually obtained by thermal evaporation from an effusion cell. See also Knudsen cell. 

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