Gallium arsenide layers

The growth of a germanium epitaxial film as an interlayer between a gallium arsenide layer and a silicon layer has received attention in the microelectronics industry. Epitaxial gemianium is also an important material in the fabrication of tandem solar cells. The growth of germanium films can be accomplished by CVD. A propo.sed mechanism is... 

The semiconductor laser is composed of several layers of semiconducting materials that have different compositions and are sandwiched between a heat sink and a metal conductor a typical arrangement is represented schematically in Figure 21.17. The compositions of the layers are chosen so as to confine both the excited electrons and holes, as well as the laser beam, to within the central gallium arsenide layer. 

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

C2.18.4.1 HOMOEPITAXY OF GALLIUM ARSENIDE BY ATOMIC LAYER EPITAXY... 

The first semiconductor lasers, fabricated from gallium arsenide material, were formed from a simple junction (called a homojunction because the composition of the material was the same on each side of the junction) between the type and n-ty e materials. Those devices required high electrical current density, which produced damage ia the region of the junction so that the lasers were short-Hved. To reduce this problem, a heterojunction stmcture was developed. This junction is formed by growing a number of layers of different composition epitaxially. This is shown ia Figure 12. There are a number of layers of material having different composition is this ternary alloy system, which may be denoted Al Ga his notation, x is a composition... 

With gallium arsenide, additional elements, such as Si, S, and Cl, are of interest because of their doping character. Impurity levels on the order of lO cm are encountered with commercial substrates, which can be readily assessed using direct TXRF." VPD-TXRF is not possible in this case because of the lack of a native oxide layer on gallium arsenide. 

A schematic of epitaxial growth is shown in Fig. 2.11. As an example, it is possible to grow gallium arsenide epitaxially on silicon since the lattice parameters of the two materials are similar. On the other hand, deposition of indium phosphide on silicon is not possible since the lattice mismatch is 8%, which is too high. A solution is to use an intermediate buffer layer of gallium arsenide between the silicon and the indium phosphide. The lattice parameters of common semiconductor materials are shown in Fig. 2.12. 

Cachet H, Cortes R, Froment M, Mamin G (1999) Epitaxial growth of electrodeposited cadmium selenide on (111) gallium arsenide. Philos Mag Lett 79/10 837-840 Muthuvel M, Stickney JL (2006) CdTe Electrodeposition on InP(lOO) via Electrochemical Atomic Layer Epitaxy (EC-ALE) Studies Using UHV-EC. Langmuir 22 5504-5508 Streltsov EA, Osipovich NP, Ivashkevich LS, Lyakhov AS (1999) Effect of Cd(ll) on electrodeposition of textured PbSe. Electrochim Acta 44 2645-2652 Beaunier L, Cachet H, Cortes R, Froment M (2000) Electrodeposition of PbSe epitaxial films on (111) InP. Electrochem Commun 2 508-510... 

Villegas, I. Stickney, J. L. 1992. Preliminary studies of gallium arsenide deposition on gold (100), (110), and (111) surfaces by electrochemical atomic layer epitaxy. J. Electrochem. Soc. 139 686-94. 

Silicon is the most popular material for photovoltaic (PV) power. Another material is gallium arsenide (GaAs), which is a compound semiconductor. GaAs has a crystal structure similar to that of silicon, but it consists of alternating gallium and arsenic atoms. It is well suited for PV applications since it has a high light absorption coefficient and only a thin layer of material is required, which reduces the cost. 

In one method, arsenic(III) chloride (AsCf, boiling temperature 376 K) is used to transport gallium vapour to the reaction site where gallium arsenide is deposited in layers. The reaction involved is ... 

The gallium arsenide laser actually contains a layer of GaAs sandwiched between layers ofp and /J-type gallium aluminum arsenide (Gai- AfAs). As depicted in Figure 8.12, the band gap of gallium aluminum arsenide is larger than that of gallium arsenide. 

A chemical species on the top-most layer of the solid (i.e., a surface species) occupies a site. For example, an arsine molecule adsorbed on a surface occupies a site, and could be denoted AsH3(s). Another example of a surface species is a bare gallium atom, Ga(s), on the top layer of a gallium arsenide crystal. What happens if another species, say a gas-phase AsH3, lands on top of the Ga(s) As shown in Fig. 11.3, the gallium atom that was at the surface is buried it is no longer designated a surface species. In this nomenclature it has become a bulk species. 

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