Gallium-arsenide

The most widely used of the ni-V and It-VI materials is gallium arsenide, which is emerging as an important complement to silicon.Compared to silicon, it has the following advantages  

For all its advantages, gallium arsenide has yet to be used on any large scale, at least outside optoelectronic applications. The reasons are cost (over ten times that of silicon), small wafer size, low thermal conductivity (1/3 that of silicon), and low strength. 

Gallium arsenide is epitaxially deposited on a silicon substrate and the resulting composite combines the mechanical and thermal properties of silicon with the photonic capabilities and fast electronics of gallium arsenide. 

INTRODUCTION This data sheet contains information for intrinsic single crystal gallium arsenide. 

MECHANICAL PROPERTIES, (298°K) Young s Modulus, (psi) not available Hardness, (Knoop) 750  

Transmission Region, (External Transmittance 10% with 2. 0 mm. thickne s s) 1.0 - 15ui  

Hirschmann, andT.E. Walsh, Report No. NASA TN D-4049, (June 1967). 

In principle, the same basic methods of heat treatment, ion bombardment and cleavage which are used to produce clean silicon surfaces can be used to generate clean GaAs surfaces, and the same general reservations apply. However, the fact that GaAs is a compound whose surface stoichiometry is potentially variable introduces additional problems for those techniques which depend on removal of material. Cleavage is not subject to these effects, however, and the cleavage plane is 110, which contains equal numbers of Ga and Aa atoms. Furthermore, the cleaved surface structure does not appear to be metastable, at least in terms of the LEED patterns produced [106], so in some ways it represents a simpler case than silicon. 

Ion bombardment could result in the preferential sputtering of one element, but there is no direct evidence for this [107]. In order to anneal out the damage, however, temperatures 1000 K are necessary, so stoichiometric changes can still occur and for this reason, ion bombardment with much lower temperature anneals ( 750 K) has frequently been used (e.g. ref. 107). It is known, however, that this treatment produces a surface with substantially modified properties, leading, for example, to changed evaporation behaviour [108]. 

There is no doubt that heat treatment can result in the preferential loss 

An alternative technique for producing clean surfaces of any orientation of III—V compounds and alloys is to grow a thin epitaxial film ( 2000 A) in situ from molecular beams of the elements generated from Knudsen sources inside the UHV system. The growth process has become known as molecular beam epitaxy or MBE [111]. Any impurities remain at the film—substrate interface and the freshly created surface is very clean. A more detailed account of this process will be given in Sect. 5. 

Finally, as with silicon, field desorption has been used on GaAs to produce clean field emitters [112] with fields of 1.4—2.7 x 108 V cm-1, followed by annealing at temperatures up to 620 K. Temperatures higher than this produced considerable surface roughening and evidence of surface migration, occuring most readily on (lll)B faces, was observed at 520 K. 

Epitaxial GaAs layers 10 /im thick were deposited on (100) n-type (0.05 n cm) GaAs substrates. 

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Figure B3.2.11. Total energy versus lattice constant of gallium arsenide from a VMC calculation including 256 valence electrons [118] the curve is a quadratic fit. The error bars reflect the uncertainties of individual values. The experimental lattice constant is 10.68 au, the QMC result is 10.69 (+ 0.1) an (Figure by Professor W Schattke).

Jin C, Taylor K J, Conoeioao J and Smalley R E 1990 Ultraviolet photoeleotron speotra of gallium arsenide olusters Chem. Phys. Lett. 175 17... 

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. 

Kher S S and Wells R L 1996 Synthesis and characterization of colloidal nanoorystals of capped gallium arsenide Nanostruct. Mater. 7 591... 

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

G. B. SttingfeUow, ed., "GaUium, Arsenide, and Related Compounds, 1991," iu the Proceedings of the Eighteenth International Symposium on Gallium, Arsenide, and Belated Compounds, Sept. 9—12, 1991, Seattle, Wash., Institute of Physics, Bristol, U.K., 1992. 

T. Sugano, ed.. Gallium, Arsenide, and Belated Compounds, No. 63, Institute of Physics, Bristol, U.K., 1982. 

D. P. Perry, Gallium, Arsenide Technology, McMillan Co., New York, 1985. 

M. J. Howes andD. V. Morgan, Gallium Arsenide Materials, Devices, and Details,JohnWHey 8c Sons, Ltd., Chichester, U.K., 1985. 

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... 

Fig. 12. Details of an aluminum gallium arsenide semiconductor diode laser.

An important development in the 1980s was the multiple stripe laser, capable of emission of high output powers. A number of stripes are placed on a bar perhaps 1 cm wide the output of the different stripes is coupled so that the device may be regarded as a single laser. Bars having continuous output up to 20 W are available in the aluminum gallium arsenide system. A number of bars may then be stacked to form two-dimensional arrays with high values of output power. 

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