Vapor Phase Epitaxy VPE

Other techniques include closed space vapor transport, sol-gel and other solution technologies, such as self-aligning molecular epitaxy. Closed space vapor transport relies on localized heating of sources, generally elemental, to evaporate them, and a cool zone at which a film or bulk crystal is deposited. A variation of this technique has been used to grow II-VI crystals on the space shuttle. This technique has difficulty controlling uniformity, dopant levels, and multiple layer structures among other issues. 

Two recent techniques that have come to be applied to compound semiconductors and oxides are pulsed laser deposition (PLD) also known as laser ablation [6] and ion beam assisted deposition (IBAD) [2-8]. These techniques have been developed for films whose elemental constituents are not easily volitalized in elemental or organome-tallic forms or whose formation can benefit from the added energy imparted to the reactants by the process. 

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The primary methodologies for forming thin-film materials with atomic level control are molecular beam epitaxy (MBE) [4-9], vapor phase epitaxy (VPE) [10-12], and a number of derivative vacuum based techniques [13]. These methods depend on controlling the flux of reactants and the temperature of the substrate and reactants. 

There are numerous materials, both metallic and ceramic, that are produced via CVD processes, including some exciting new applications such as CVD diamond, but they all involve deposition on some substrate, making them fundamentally composite materials. There are equally numerous modifications to the basic CVD processes, leading to such exotic-sounding processes as vapor-phase epitaxy (VPE), atomic-layer epitaxy (ALE), chemical-beam epitaxy (CBE), plasma-enhanced CVD (PECVD), laser-assisted CVD (LACVD), and metal-organic compound CVD (MOCVD). We will discuss the specifics of CVD processing equipment and more CVD materials in Chapter 7. 

Fig. 4. Energy below the conduction band of levels reported in the literature for GaP. States are arranged from top to bottom chronologically, then by author. At the left is an indication of the method of sample growth or preparation liquid phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), irradiated with 1-MeV electrons (1-MeV e), and vapor phase epitaxy (VPE). Next to this the experimental method is listed photoluminescence (PL), photoluminescence decay time (PLD), junction photocurrent (PCUR), photocapacitance (PCAP), transient capacitance (TCAP), thermally stimulated current (TSC), transient junction dark current (TC), deep level transient spectroscopy (DLTS), photoconductivity (PC), and optical absorption (OA).

Hamilton et al. (1979) have shown that a level at 0.75 eV above the valence band (M1 in Figs. 5 and 7) is the dominant recombination center in epitaxial layers and controls the minority-carrier lifetime in -type GaP. Another state at v + 0.92 eV has been shown to be caused by the persistent presence of Ni in vapor phase epitaxial (VPE) GaP (Dean et al, 1977). 

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). 

Methods of manufacturing mercury cadmium telluride material have evolved from bulk melt growth to liquid phase epitaxy (LPE) technology, vapor phase epitaxy (VPE) and metal-organic chemical vapor deposition (MOCVD) [5-7], These new methods have made it possible to manufacture large two-dimensional focal plane arrays [8-11],... 

Pyrophoric A compound that reacts with air in a way that results in spontaneous ignition. m-V compound semiconductor A semiconductor that in pure form is composed of a mixture of atoms of one or more elements from Column III and an equal number of atoms of one or more elements from Column V of the Periodic Table. The Column III atoms are arranged on one sublattice and the Column V atoms are on another. Vapor-phase epitaxy (VPE) An epitaxial growth process that only uses chemical precursors that are delivered to the growing surface in the vapor-phase. 

For silicon, the process can be used to grow films with thicknesses of 1 jtimto >100 nm. Some processes require high substrate temperature, whereas others do not require significant heating of the substrate. For photovoltaic applications, epitaxial silicon is usually grown using liquid-phase epitaxy (LPE) [1-3] and vapor-phase epitaxy (VPE) [4-6], which is a modification of chemical vapor deposition (CVD). 

As mentioned above, CVD, the most general term describing the deposition process, implies nothing about the crystallinity of the grown layer. Epitaxy is directed at single crystal layers on single crystal substrates. Vapor phase epitaxy (VPE) was coined to parallel liquid phase epitaxy (LPE). 

Figure 4-8. Typical vapor phase epitaxy (VPE) system.

There are several technologies for creating the conditions inside a reactor needed to support epitaxial growth, of which the most important is Vapor Phase Epitaxy (VPE). In this process, a number of gases are introduced in an induction heated reactor where only the substrate is heated. The temperature of the substrate typically must be at least 50 % of the melting point of the material to be deposited. 

Vapor Phase Epitaxy (VPE) Gallium Arsenide AsClj/H2/Ga... 

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