^\y^:?^ : :/mk'^kk^ JL°^ * * v •J&fr \> 4L* *;*&*> ^ - v . *^o^ - \* * ^ >*- aN V *j CEMENTATION LIQUID-SOLID SEPARATION H S' i -^Cement copper GERMANIUM PRECIPITATION LIQUID -SOLID SEPARATION Recycle organic Precipitate to 'germanium recovery SOLVENT EXTRACTION STRIPPING NHi GALLIUM PRECIPITATION LIQUID-SOLID SEPARATION I Ferrous sulfate solution _^Zinc sulfate solution Gallium hydroxide PURIFICATION ELECTROLYSIS ▼ Crude gallium Figure 4.— Gallium recovery from Musto Explorations Ltd.'s mine near St George, UT. zinc are stripped from the organic phase, and ammonia is injected into the stripped solution to precipitate gallium hydroxide. Gallium hydroxide precipitate is separated from the zinc solution and purified, and 99.999-pct-pure (5N) gallium metal is recovered by electrolysis. The elec- trolytic technology used at Musto's plant is proprietary technology licensed from Cominco Ltd. In July 1987 Elkem A/S of Norway began producing crude gallium using aluminum smelter flue dust as a source material. Dusts generated at two smelters in Mosjoen and Tyssedal are blended to yield material with the following average concentration: Carbon, 33 pet; fluo- rine, 17 pet; oxygen, 17 pet; aluminum, 13 pet; sodium, 9 pet; iron, 6 pet; sulfur, 3 pet; calcium, 1.5 pet; and gal- lium, 0.5 pet. Leaching the flue dust with hydrochloric acid extracts the gallium. Solids are filtered from the liquid phase and mixed with portland cement before disposal. The liquid phase undergoes a series of solvent extraction stages to separate gallium from dissolved impurities. After cleaning and stripping, crude gallium is recovered by electrolysis of the water phase. A simplified flowsheet for this process is shown in figure 5. GALLIUM PURIFICATION For most applications, purity requirements for gallium are either 6N or 7N. Crude gallium is purified in essen- tially two steps-the first step produces 99.99-pct-pure (4N) gallium, and the second produces 6N to 7N metal. Many of the impurities in crude gallium occur in the surface oxide or as finely dispersed phases in the metal. Liquid gallium filtration and heating under vacuum remove these types of impurities. Metallic impurities can be reduced to less than 0.01 pet, producing 4N gallium, by sequential washing with hydrochloric acid. Another method that can be used is electrolytic refining, which involves anodic dissolution of gallium in an alkaline solu- tion, and then deposition at a liquid gallium cathode. The principal method used to produce 6N and 7N metal is gradual crystallization of molten gallium. In this pro- cess, impurities remain in the liquid phase and do not con- taminate the gallium crystal. Crystallization is repeated until gallium of the desired purity is obtained. Another method of producing high-purity gallium is to convert the gallium to a halide compound, such as gallium trichloride, which is then zone-refined. High-purity gallium is recovered by electrolysis of the halide compound. GALLIUM ARSENIDE FABRICATION GaAs single crystals are more difficult to fabricate than those of silicon. With silicon, only one material needs to be controlled, whereas with GaAs, a one-to-one ratio of gallium atoms to arsenic atoms must be maintained. At the same time, arsenic volatilizes at the temperatures needed to grow crystals. To prevent a loss of arsenic, which would result in the formation of an undesirable gallium-rich crystal, GaAs ingots are grown in an enclosed environment to contain the arsenic. Two basic methods are used to fabricate GaAs single- crystal ingots-the boat-growth, horizontal Bridgeman (HB) or gradient freeze technique, and the liquid-encapsulated Czochralski (LEC) technique. Ingots produced by the HB method are D-shaped and have a typical cross-sectional area of about 2 in 2 . By contrast, single-crystal ingots grown by the LEC method are round and are generally 3 in in diameter, with a cross-sectional area of about 7 in . In HB growth, gallium and arsenic in the proper ratio are placed in one end of a silicon dioxide (quartz) or pyrolytic boron nitride boat. A seed GaAs crystal is contained at the other end of the boat. The boat is placed in a sealed quartz tube, which is evacuated to a very low pressure. The tube is placed in a multiple-zone furnace, where the gallium and arsenic react to form GaAs. The 12 A .umlnum smelter flue dust LEACHING HC1 1 LIQDID-SOLID SEPARATION ^ r> : J 1 4 SOLVENT EXTRACTION Recycle organic 1 f STRIPPING ^ 1 r ELECTROLYSIS ^ « *i v 1 Crude r gallium Figure 5.— Elkem A/S process for recovering gallium from aluminum smelter flue dust compound is heated to 1,240° C, the melting point of GaAs. The GaAs melt is slowly cooled from the seed end, resulting in single-crystal growth. In the LEC method of crystal growth (fig. 6), carefully weighed pieces of gallium and arsenic are melted in a pressurized vessel (crystal puller). The GaAs melt is contained in a crucible con- structed of either high-purity quartz or pyrolytic boron nitride. The melt is covered with a layer of boric oxide, which retards arsenic loss from the melt by sublimation. A seed crystal is lowered through the boric oxide into the melt and slowly withdrawn as both the seed and crucible are rotating. Each of these methods produces GaAs ingots with par- ticular advantages and disadvantages. Crystals formed by the boat-growth method are particularly suitable for opto- electronic applications because their structure is highly perfect with respect to dislocations. Optoelectronic devices also require crystals with a high doping concentration, which boat-grown crystals readily provide, because the silicon dissolved from the quartz boat contributes to crystal doping. This latter benefit becomes a problem if semi- insulating GaAs crystals for ICs are being produced. The silicon impurities are called shallow donors, or N-type dopants. To compensate for these impurities, either a controlled quantity of gallium oxide can be added to the melt, or chromium, a deep acceptor or P-type dopant, can be added. Crystal growth also can be accomplished in a boron nitride container, which eliminates any contact with silicon-containing material during growth. The shape of the HB-grown ingot makes it inconvenient for subsequent wafer processing, because automated wafer processing sys- tems are designed to handle round wafers. LEC-grown ingots generally contain more crystal structure defects, i.e., they have higher dislocation densities, than HB-grown ingots. This affects the electronic properties of the device constructed on the GaAs. Dislocation densities in HB wafers normally run between 500 and 20,000 per square centimeter; those in LEC wafers can be as large as 100,000 per square centimeter. Because chips are batch processed, wafer by wafer, the larger the wafer, the more chips per wafer, and the lower the cost per chip. A 3-in-diameter LEC-grown wafer can yield more of the same-size chips than a 2- by 1.5-in HB wafer. Conversely, the capital costs for an HB system are significantly less than those for an LEC system. After the ingots are grown, the ends are cut off, and the ingots are shaped by grinding the edges. Ingots are then sliced into wafers (fig. 7). Wafers go through several stages of surface preparation, polishing, and testing before they are ready for device manufacture or epitaxial growth. Wafer preparation steps are done in a clean room and with minimal contact to avoid introducing surface contami- nants. In LEC growth, the effective yield from starting material to finished wafers is currently less than 15 pet. Pure GaAs is semi-insulating, which means that it is not a conductor of electricity. In order for GaAs to conduct electricity, a small number of atoms of another element must be incorporated into the GaAs crystal structure. This is called doping. These atoms act as electron donors or electron acceptors. Electron donor atoms have one more electron than the atoms that they are replacing, and this electron is free to move within the crystal as an electrical charge carrier. Electron acceptors have one less electron than the atoms they are replacing and behave as positively charged particles to serve as electrical charge carriers (5). To manufacture devices from GaAs wafers, the wafers must be doped with another metal or metals. Normally, this is accomplished either by ion implantation or by some type of epitaxial growth. Because GaAs is a semi- insulating substrate, no special isolation areas are required to separate each device fabricated on the chip. This results in more compact, higher density circuits, which add to GaAs's speed advantage. In ion implantation, ions of another metal are implanted into specific areas of the semi-insulating GaAs to make those areas electronically active. Areas of the chip that are to remain semi-insulating are covered with a photoresist mask before ion implantation. The process of ion implantation may be repeated several times with dif- ferent metals on different areas of the chip, depending on the type and complexity of the device being manufactured. After ion implantation, the GaAs must be annealed at about 850° C in order to activate the implanted dopants and remove crystal damage incurred during implantation. When annealing, as in crystal growth, several techniques, including encapsulation of the chip, are used to prevent arsenic losses at the elevated temperature. After doping, optoelectronic device or IC manufacture can be completed through deposition of layers of metals and insulators by various techniques. A similar technique, called ion cluster beam, is not as frequently used as ion implantation. In this technique, ions are grouped together and implanted into the wafer at 13 Figure 6.-GaAs Ingot growing in LEC furnace (Courtesy Morgan Semiconductor Div. of Ethyl Corp.) Figure 7.-LEC-grown GaAs Ingot and wafers (Courtesy Morgan Semiconductor Div. of Ethyl Corp.) 14 lower speeds than used in ion implantation. This process is reported to result in less damage to the crystal structure. The deposition of an epitaxial layer is another means of creating electronically active regions on the GaAs substrate. There are four principal methods for growing epitaxial layers-liquid-phase epitaxy (LPE), vapor-phase epitaxy (VPE), metal-organic chemical vapor deposition (MOCVD), and molecular beam epitaxy (MBE). LPE is an earlier method of epitaxy that is generally not considered suitable for complex semiconductor production because it cannot be as precisely controlled as the other three techniques. In LPE, the substrate wafer is contained in a graphite boat within a quartz furnace tube, where it is contacted with solutions containing the metals to be deposited. Cooling the solution causes the metals to precipitate on the substrate. LPE produces relatively thick epitaxial layers, and the boundaries between layers are gradual rather than sharply defined. Two methods of VPE are used to grow epitaxial layers on a GaAs substrate-the hydride method and the chloride method. In VPE, GaAs substrates are mounted in a reactor. To make GaAsP epitaxial layers, two gaseous streams are introduced into the reactor. In the hydride process, one gas stream combines arsine (AsH 3 ) and phosphine (PH 3 ) with a hydrogen carrier gas; the other gas stream is a hydrochloric acid gas that has been passed over a gallium reservoir to form gallium trichloride, and that also is mixed with a hydrogen carrier gas. Dopants are added to the gas streams if necessary. Gallium trichloride reacts with the AsH 3 and PH 3 gases to deposit a GaAsP layer on the substrate. In the chloride process, arsenic trichloride and phosphorus trichloride gases are substituted for AsH 3 and PH 3 . VPE technology can coat multiple wafers at the same time, and the layer thickness, molecular composition, and dopant concentration can be more closely controlled than with LPE. In MOCVD, wafers are placed in a quartz reactor, maintained at atmospheric or slightly reduced pressure and at a temperature between 650° and 750° C. Metals to be deposited are in the forms of gases that chemically com- bine on the heated substrate. For example, to prepare a GaAlAs layer, gallium and aluminum are present in the form of organic gases, generally trimethyl or triethyl gallium and aluminum [(CH 3 ) 3 Ga or (C 2 H 5 ) 3 Ga and (CH 3 ) 3 A1 or (QILJjAl] in a hydrogen carrier gas. Arsenic is in the form of AsH 3 in the hydrogen carrier gas. Dopants may also be added. The flow rates of these gases are carefully controlled. As the gases mix in the reactor and contact the hot wafers, they react to form GaAlAs and methane or ethane, and the GaAlAs deposits on the substrate wafers. With MBE, the GaAs substrate is mounted on a heating block in a reactor maintained under a vacuum, along with effusion cells containing the elements to be deposited. For a GaAlAs layer, the effusion cells would contain gallium, aluminum, arsenic, and dopants. The elements are heated to temperatures that cause them to evaporate. By precise opening and closing of mechanical shutters in front of the effusion cells, the concentration of each element as it deposits can be carefully controlled. With both MOCVD and MBE, the process may be repeated to build many thin layers of materials with dif- fering compositions. After the epitaxial layers are depos- ited, device manufacture can be completed through depo- sition of metallic and insulating layers (fig. 8). As with crystal growth methods, both MOCVD and MBE have advantages and disadvantages. MOCVD can coat multiple wafers at a time, whereas MBE systems can coat only one. MBE requires a vacuum, while MOCVD can be performed at atmospheric pressure. The cost of MOCVD equipment is approximately one-third the cost of MBE equipment ($250,000 compared with $800,000). MBE provides the most precise control over the compo- sition and thickness of the epitaxial layers, and it also pro- vides the greatest reproducibility. MOCVD uses AsH 3 gas, which requires a room equipped with safety equip- ment to prevent the toxic gas from escaping. GBL GigaBit Logic INCHES Figure 8.— GaAs wafer with devices (Courtesy GigaBit Logic Inc.) 15 SECONDARY RECOVERY Because of the low yield in processing gallium to optoelectronic devices or ICs, substantial quantities of new scrap are generated during the various processing stages. These wastes have varying gallium and impurity contents, depending upon the processing step from which they result. GaAs-based scrap, rather than metallic gallium, represents the bulk of the scrap that is recycled. During the processing of gallium metal to a GaAs device, waste is generated during the GaAs ingot formation. If the ingot formed does not exhibit single-crystal structure or if it contains excessive quantities of impurities, it is considered to be scrap. Also, some GaAs remains in the reactor after the ingot is produced and may be recycled. During the wafer preparation and polishing stage, significant quantities of wastes are generated. Before wafers are sliced from the ingot, both ends of the ingot are cut off and discarded, because impurities are concentrated at the tail end of the ingot and crystal imperfections occur at the seed end. These ends represent up to 25 pet of the weight of the ingot. As the crystal is sliced into wafers, two types of wastes are generated-saw kerf, which is essentially GaAs sawdust, and broken wafers. When the wafers are polished with an abrasive lapping compound, a low-grade waste is generated. During the epitaxial growth process, various wastes are produced, depending on the growth method used. In LPE, metallic gallium contaminated with arsenic and dopant metals results, and in VPE, exhaust gases containing GaAs are produced. Because GaAs is a brittle material, wafers may break during the fabrication of electrical circuitry on their surfaces. These broken wafers also may be recycled. Gallium content of these waste materials ranges from less than 1 pet to 99.99 pet. LPE wastes normally have the highest gallium content, 98 to 99.99 pet. Ingot ends and wafers broken during processing generally contain 39 to 48 pet gallium, VPE exhaust gases contain 6 to 15 pet gallium, saw kerf contains up to 30 pet gallium (wet basis), and lapping compound wastes contain less than 1 pet gallium. These wastes are contaminated with small quantities of many impurities, the most common being aluminum oxide, copper, chromium, germanium, indium, silicon, silicon carbide, tin, and zinc. Wafers broken during the fabrication of electrical circuitry also contain gold and silver impurities. In addition to metallic impurities, the scrap may be contaminated with materials introduced during processing such as water, silicone oils, waxes, plastics, and glass. In processing GaAs scrap, the material is crushed, if necessary, and then dissolved in a hot acidic solution. This acid solution is neutralized with a caustic solution to precipitate the gallium as gallium hydroxide, which is filtered from the solution and washed. The gallium hydroxide filter cake is redissolved in a caustic solution and electrolyzed to recover 3N to 4N gallium metal. This metal may be refined to 6N or 7N gallium by conventional purification techniques if desired. Some GaAs manufacturers recycle their own scrap, or scrap may be sold to metal traders, to a company that specializes in recycling GaAs, or to the GaAs manufac- turer's gallium supplier, who can recover the gallium and return it to the customer. Generally the prices com- manded by GaAs scrap parallel the price fluctuations of 4N gallium metal. Also, prices are dependent on the type and gallium content of the scrap; saw kerf sells for a lower price than ingot scrap, which in turn sells for a lower price than metallic (LPE) scrap. Although GaAs scrap is an important component of the gallium materials flow throughout the world, it cannot be considered an additional long-term source of world gallium supply. GaAs scrap that is recycled is new scrap, which means that it has not reached the consumer as an end product and is present only in the closed-loop operations between the companies that recover gallium from GaAs scrap and the wafer and device manufacturers. Because this closed loop occasionally crosses international boundaries, it is difficult to distinguish between gallium recovered from scrap and virgin gallium when evaluating the gallium supply of an individual country. For example, GaAs scrap generated in the United States and Canada may be processed to recover 4N gallium in Canada. The 4N gallium is shipped to Switzerland for refining to 7N gallium, which is then exported to the United States. In this situation, the gallium received in the United States from Switzerland appears to be a new source of supply, while in fact a portion of this gallium originated as GaAs scrap from the United States. 16 WORLD SUPPLY AND DEMAND Little information is published detailing gallium produc- quantities of gallium are exported from either the United tion and trade data. The United States and Japan are the States or Japan, but significant trade in GaAs occurs, only countries for which detailed data are available. Also Some GaAs scrap is exported from the United States to in many cases, no distinction is made in published figures the Federal Republic of Germany for gallium recovery, between virgin, recycled, and purified gallium. As an and Japan is believed to export significant quantities of example, the United States ships some GaAs scrap to the GaAs substrate wafers to the United States. However, Federal Republic of Germany for gallium recovery, and because the value of these items is very small when the the recovered gallium is returned to the United States. value of the entire U.S. trade is considered, they are not This gallium may be counted twice as a part of the domes- classified separately. So the trade patterns of these mate- tic supply. Or, one country recovers virgin gallium and rials cannot be quantitatively determined, ships it to a second country for refining to 7N gallium. In addition to gallium metal and GaAs trade, the Each country may count this as production, thus doubling United States imports many of its consumer electronics the quantity of gallium that appears to be available. Con- goods and automobiles. Many of these items, such as sequently, determination of gallium supply-demand figures compact disk players, televisions, calculators, and video is subject to significant interpretation. cassette recorders, contain GaAs components in the form of LEDs and laser diodes. Here again, significant quan- PRODUCTION tides of gallium compounds may be imported, but cannot be quantitatively determined. Tables 3 and 4 show estimates of both primary and sec- ondary gallium production. These figures were derived DOMESTIC DEMAND from U.S. production data, published by the Bureau of Mines; U.S. import data, supplied by the Department of U.S. supply-demand relationships, shown in table 7, Commerce; and production and import data for Japan, indicate that most of the domestic demand for gallium has published in RoskilTs Letter From Japan. Because most been supplied by imports. Before 1983, the Aluminum Co. of the world's gallium demand centers in Japan and the of America (Alcoa) and Eagle-Picher Industries Inc. United States, these sources are believed to provide data recovered primary gallium in the United States. But after on about 85 pet of the gallium produced in the world. 1983, no primary gallium was produced until 1986, when Musto Explorations began recovering a small quantity of TRADE gallium from its mine in Utah. Over 90 pet of the gallium consumed in the United Import data for the United States and Japan are shown States is classified as "instruments." This category includes in tables 5 and 6. Historically, the United States has gallium consumed in optoelectronic devices, in ICs, and in received most of its gallium from France, the Federal some research and development activities. The remainder, Republic of Germany, and Switzerland, while Japan's prin- classified as "other," consists of gallium consumed in other cipal import sources have been China, France, and the research and development activities and in specialty alloys. Federal Republic of Germany. No data are published Optoelectronic devices represent most of the gallium separately detailing gallium exports from the United demand in the United States. States, Europe, or Japan. It is believed that no significant Table 3. - World primary gallium production" (Kilograms) Country 1980 1981 1982 1983 1984 1985 1986 1987 China 3,000 3,400 2,600 5,100 3,500 5,000 6,000 6,000 Czechoslovakia 500 1,650 1,700 2,000 2,500 3,300 3,000 3,200 France 4,300 4,600 3,700 7,000 8,500 9,500 15,500 14,000 Germany, Federal Republic of 2,300 3,000 4,000 5,300 6,000 5,500 7,000 7,000 Hungary 1,500 1,500 2,000 3,000 3,000 2,800 3,200 3,000 Japan 3,000 3,000 3,000 3,000 10,000 10,000 10,000 5,000 Norway 500 United States 3,000 1,500 1,560 l '750 W Total 17,600 18,650 18,560 25,400 33,500 36,100 45,450 ^^OO 'Estimated. W Withheld to avoid disclosing individual company proprietary data. 'Reported figure. 2 Excluding U.S. production. 17 Table 4. - World secondary gallium production (Kilograms) e 1 Country Canada Germany, Federal Republic of Japan United Kingdom United States Total 'Estimated. *New scrap only. 1980 1981 1982 1983 1984 1985 1986 1987 500 500 700 1,000 2,100 1,500 1,500 3,000 5,000 4,000 5,000 7,000 4,000 9,000 200 300 800 1,000 1,000 1,000 1,500 3,700 5,800 5,500 7,000 10,100 6,500 12,000 5,000 1,500 7,000 1,500 2,400 17,400 Table 5. - U.S. /gallium imports for consumption, by country (Kilograms) Country 1977 1978 1979 1980 1981 1982 1983 Belgium-Luxembourg 200 Canada 276 75 450 1,449 589 379 279 China 409 916 500 Congo Czechoslovakia 53 France 232 386 480 829 Germany, Federal Republic of ... 774 748 218 561 585 1,448 918 Hungary 37 59 India 10 Italy 349 98 Japan 41 13 48 146 Malaysia 100 2 Netherlands 41 New Zealand Singapore Spain 148 Suriname Sweden 1 Switzerland 1,485 2,628 5,498 3,444 2,679 2,429 4,154 Taiwan 11 United Kingdom 133 41 56 70 267 468 Total 2,884 3,721 6,401 6,175 5,536 5,199 7,294 Source: U.S. Department of Commerce. 1984 1985 1986 1987 55 1 3 98 107 400 10 2,449 1,563 8,231 6.364 1,554 1,423 2,740 1,215 168 17 1 13 89 105 123 451 5 40 131 50 132 21 30 96 201 5 4,088 4,268 5,640 4,081 50 651 163 348 142 9,669 7,961 17,202 12,490 Table 6. - Japanese/gallium imports, by country (Kilograms) Country ^980 1981 Canada China 2,500 2,400 Czechoslovakia 500 France 10 2,000 Germany, Federal Republic of .... 1,200 1,800 Hungary 10 600 Switzerland 1 ,400 300 U.S.S.R _0 0_ Total 5,120 7,600 Source: Roskill's Letter From Japan and Rare Metals News. 1982 1983 1984 1985 1986 1987 2,600 1,260 1,400 2,100 1,600 120 4,600 480 2,800 3,720 2,300 100 200 2,800 900 3,100 5,450 1,500 85 4,000 2,285 5,264 3,200 1,800 50 9,080 14,200 13,835 16,599 300 5,100 450 2,700 4,200 750 100 13,600 300 2,000 1,100 5,600 4,900 1,500 740 16,140 18 Table 7. - Gallium supply-demand relationships, 1 977-87 (Kilograms) 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 WORLD PRODUCTION United States W e 5,500 e 2,600 e 3,000 e 1,500 e 1,560 e e 9,500 e 14,600 e 17,150 c 17,100 e 25,400 e e 33,500 e 36,100 750 e 44,700 W Rest of world W e 6,650 e 38,700 Total' 12,420 12,200 12,100 17,600 18,650 18,660 25,400 33,500 36,100 45,450 ^JOO COMPONENTS AND DISTRIBUTION OF U.S. SUPPLY e 2,600 6,401 e 2,000 e 3,000 6,175 e 1,800 e 1,500 5,536 e 1,900 e 1,560 5,199 e 1,900 •11,001 c 10,975 8,936 8,659 c 9,149 11,499 8,887 19,158 e 1,900 e 265 8,810 Components of U.S. supply: Production W c 5,500 Imports 2,884 3,721 Industry stocks, Jan. 1 _ W e 1,950 Total 11,054 11,221 Distribution of U.S. supply: Industry stocks, Dec. 31 e 1,950 e 2,000 Exports e 315 e 313 Demand 8,789 8,908 7,965 8,305 824 603 8,789 8,908 Estimated. NA Not available. W Withheld to avoid disclosing company proprietary data. 'Excluding U.S. production. STRUCTURE OF THE INDUSTRY e o 7,294 1,855 e 9,669 1,830 7,961 926 750 17,202 1,206 e 1,800 e 151 9,050 e 1,900 e 226 6,810 e 1,855 e 157 6,647 1,830 926 e 894 e 3,513 6,425 7,060 W 12,490 813 W 1,206 813 732 c 285 e 2,302 NA 7,396 16,043 10,729 U.S. DEMAND PATTERN Instruments Other 7,965 824 8,305 603 8,398 8,105 6,299 652 705 51 1 6,124 523 5,915 510 6,320 740 7,071 325 14,920 1,123 10,397 332 Total U.S. demand .... 8,789 8,908 9,050 8,810 6,810 6,647 6,425 7,060 7,396 16,043 10,729 Because gallium is a byproduct metal and undergoes many refining and processing stages before a marketable product is produced, gallium is truly an international business. Most bauxite is mined in Australia, Africa, and South America, while gallium recovery and refining are currently centered in Europe. GaAs wafer and device fabrication is concentrated in the United States and Japan. Many gallium producers have the facilities to recover 3N and 4N gallium and refine it to higher purity. Some gallium producers also have scrap recycling facilities. Table 8 shows current and projected capacities for each company that is involved in recovering, recycling, or purifying gallium metal, or has announced plans to construct new facilities. Virgin and recycle gallium plants produce 3N to 4N gallium, while purification plants yield gallium of 6N to 8N purity. Because of the nature of gallium processing, the only figures that should be considered when evaluating the long-term availability of gallium are the virgin gallium capacities. GALLIUM RECOVERY, RECYCLE, AND PURIFICATION Australia Although gallium is not currently recovered in Australia, Rhone-Poulenc of France plans to construct a 50,000-kg/yr gallium extraction plant in Pinjarra, Western Australia, to be completed by the second half of 1988. The gallium source for the operation will be the Bayer liquors generated by Alcoa of Australia Ltd.'s alumina refinery at the same location, which uses locally mined bauxite as its feed source. When this plant is completed, it will be the largest gallium extraction plant in the world, producing 4N gallium metal. Canada Alcan Aluminium Ltd. completed a 10,000-kg/yr gal- hum recycling plant at Kingston, Ontario, in early 1986. GaAs scrap from both the United States and Canada is used as feed for the plant, to produce 4N gallium. Alcan also is constructing a new facility at its Jonquiere, Quebec, alumina refinery to produce virgin gallium, which is expected to be completed in 1988. The alumina plant uses bauxite from Brazil, Guinea, and Guyana as feed material. When the plant is completed, its capacity will be 4,000 kg/yr of 4N gallium metal. Cominco recovers gallium at a 4,000-kg/yr refinery in Trail, British Columbia. Although the company also refines zinc concentrates at the same location, it does not recover gallium from these concentrates. Instead crude gallium metal, gallium oxide, scrap, and flue dust purchased from outside sources are used as plant feed to produce 6N to 7N gallium metal. China Gallium metal of 3N to 4N purity is recovered in Shangdong at the Nanding alumina plant. Bauxite is mined locally, and the gallium extraction plant has a capacity of 8,000 kg/yr. Most of the gallium produced in China is shipped to Japan for refining to 6N and 7N metal. Czechoslovakia Gallium metal is produced at the Ziar nad Hronom alumina refinery, which uses bauxite from Hungary and Yugoslavia as its raw material. At the 3,000-kg/yr plant, 3N to 4N gallium metal is produced, and most of the 19 Table 8. - World gallium plant capacities' Plant location Ownership 1987 Yearend capacity, mt 1988 1989 1990 Primary (virgin) gallium extraction plants: Australia Canada China Czechoslovakia France Germany, Federal Republic of Hungary India Japan Do Norway United States Do Do Total Secondary gallium recovery plants: Canada Do France Germany, Federal Republic of . . Do ' Japan Do Do Do Do United Kingdom United States . . Total Gallium purification plants: Canada Do France Germany, Federal Republic of Japan Do Switzerland United Kingdom United States Do Total Rhone-Poulenc SA Alcan Aluminium Ltd Shangdong Aluminium Co Czechoslovakian Government . . . Rhone-Poulenc S.A Ingal International Gallium GmbH Hungarian Aluminium Co Madras Aluminium Co Dowa Mining Co Sumitomo Chemical Co. Ltd. . . . Elkem A/S Eagle-Picher Industries Inc Musto Explorations Ltd Sulzer Brothers Inc 8 3 20 12 4 A 7 10 5 3 9 81 Alcan Aluminium Ltd Comjnco Ltd Societe Miniere et Metallurgique de Penarroya Ingal International Gallium GmbH Preussag AG Metall Dowa Mining Co Rasa Industries Ltd Sumitomo Chemical Co. Ltd Sumitomo Metal Mining Co. Ltd Ote Metal Co Mining and Chemical Products Ltd Recapture Metals Inc 10 ft 6 8 2 3 5 3 6 3 4 50 Alcan Aluminium Ltd Comino Ltd Rhone-Poulenc S.A. Ingal International Gallium GmbH . Dowa Mining Co Sumitomo Chemical Co. Ltd Alcan Aluminium Ltd Mining and Chemical Products Ltd. Eagle-Picher Industries Inc Rhone-Poulenc S.A 4 20 15 7 10 10 3 7 ~76~ 50 4 8 3 20 12 4 C) 7 10 5 3 9 15 150 10 C) 6 8 2 3 5 3 6 3 4 50 4 20 20 7 10 10 3 7 50 131 50 4 8 3 20 15 8 C) 7 10 5 3 9 15 157 10 10 6 8 2 3 5 3 6 3 4 60 5 4 20 20 7 10 10 3 7 50 136 50 4 8 4 20 20 8 3 7 10 5 3 9 15 166 10 4 10 6 8 2 3 5 3 6 3 4 64 5 4 20 20 7 10 10 3 7 50 136 Estimated. Less than 1/2 unit. gallium is exported to Japan for purification. Czechoslo- vakia plans to expand this plant's capacity to 4,000 kg/yr by 1990. France Rhone-Poulenc operates the world's largest gallium extraction plant at Salindres, with a capacity of 20,000 kg of gallium per year. Bayer liquor from Pechiney's Gardanne alumina refinery, which recovers alumina from bauxite mined locally and in Guinea, is used as feed for the gallium extraction plant. Rhone-Poulenc produces 4N gallium, which is then further refined to 6N and 7N gallium at Salindres. The bulk of this high-purity gallium is shipped to the United States and Japan. Societe Miniere et Metallurgique dc Penarroya SA. plans to increase its capacity for recycling GaAs scrap to 10,000 kg/yr by 1989. Penarroya already has a small capability to recover gallium from scrap at its plant at Noyelles-Godault. Federal Republic of Germany Ingal International Gallium GmbH operates two gallium recovery plants at Schwandorf and Lunen with a combined extraction capacity of 12,000 kg/yr. VAW's two alumina plants at the same locations, which recover alumina from bauxite mined in Australia and Guinea, supply Bayer liquor to Ingal's gallium extraction circuit. VAW's alumina refinery in Lunen is scheduled to close in 1988, but Ingal plans to construct a new 20,000-kg/yr plant in grade as a replacement, which is expected to be fully operational by mid-1989. In addition to extracting virgin gallium, Ingal also purifies its gallium to 6N to 7N purity at Schwandorf and recovers gallium from GaAs scrap. 20 Most of the high-purity gallium is exported to the United States and Japan. Preussag AG Metall operates an 8,000-kg/yr gallium recycling facility in Langelsheim to recover 3N to 4N gallium from GaAs scrap. Hungary Virgin gallium is extracted at Hungarian Aluminium Corp.'s facility in Ajka. Bayer liquor from the company's alumina refinery, which uses locally mined bauxite as its raw material, is used as the gallium source for the 4,000- kg/yr plant. Gallium of 3N to 4N purity is recovered in Hungary; most of it is shipped to Japan for refining. In 1986, Hungarian Aluminium announced that it planned to double the capacity of its plant by 1988. India Madras Aluminium Co. Ltd. began pilot-scale production of virgin gallium metal in late 1986 at its plant in Mettur, Tamil Nadu. The company's alumina refinery at the same location supplies the Bayer liquor feed stock, using locally mined bauxite as the alumina plant's raw material source. Japan Two companies in Japan, Dowa Mining and Sumitomo Chemical, produce virgin gallium, recover gallium from scrap, and produce 6N to 7N gallium metal for the Japanese market. Dowa Mining recovers gallium from zinc residues at its 7,000-kg/yr gallium extraction plant in Akita, Honshu. Zinc residues are generated at the Akita Zinc Co. Ltd. plant, which is 52 pet owned by Dowa Mining, from zinc ores mined at Akita Zinc's Uchinotai and Hanaoka Mines. Sumitomo Chemical recovers gal- hum at its 10,000-kg/yr plant in Niihama, Shikoku. Before the closure of its last operating alumina refinery in October 1986, Sumitomo Chemical used Bayer liquors from the alumina plant as its source of gallium. Both Dowa Mining and Sumitomo Chemical operate gallium purification facilities, where they produce 6N to 7N metal. In addition to refining their own productions, both companies purify imported 3N to 4N gallium, principally from China, Czechoslovakia, and Hungary. Rasa Industries Ltd. operates plants at Miyako and Osaka that recover 3N to 4N gallium from GaAs scrap. Combined plant capacity is estimated to be 3,000 kg/yr. Two other companies began operating secondary gallium recovery facilities in 1987. Ote Metal Co., a subsidiary of Mitsubishi Metal Corp., began recovering 3N to 4N gal- lium from GaAs scrap at its 6,000-kg/yr plant at the Onahama refinery in January. Sumitomo Metal Mining Co. Ltd. began operating a 3,000-kg/yr secondary gallium recovery facility in Niihama in July. Norway Elkem began operating a newly constructed gallium extraction plant at its Bremanger ferroalloy plant site in July 1987. Aluminum smelter flue dusts from primary aluminum refineries in Mosjoen and Tyssedal, containing about 0.5 pet gallium, are used as the source material for the 5,000-kg/yr plant. Only small quantities of 3N to 4N gallium have been produced at this facility. Spain Early in 1988, Rhone-Poulenc announced that it had signed an agreement with the Spanish Government to purchase the entire output of gallium-containing residues from the Aluminia Espanola SA. (Inespal) alumina refinery in San Ciprian. Although no date has been given for the start of construction, Rhone-Poulenc plans to construct a gallium extraction facility near San Ciprian. The residues are estimated to contain up to 30,000 kg/yr of gallium, but the plant capacity has not been stated. Switzerland Alcan operates a 10,000-kg/yr gallium purification plant in Rorschach, which it purchased from Swiss Aluminium Ltd. in 1985. The Rorschach plant produces gallium of 6N to 8N purity using 3N to 4N gallium recovered from scrap at the company's plant in Canada as the feed material. Most of Alcan's production is shipped to the United States, with a small quantity exported to Japan. U.S.S.R. Although no data are available to determine quantities and locations of plants that recover gallium, it is believed that the U.S.S.R. recovers, purifies, and consumes significant quantities of gallium for IC production. In 1986, it was announced that the U.S.S.R. plans to increase its production and usage of gallium, according to the 1986-90 5-year plan. United Kingdom Mining and Chemical Products Ltd. operates a 3,000- kg/yr gallium recycling facility in Alperton, Wembley, to recover gallium from GaAs scrap generated at its electronic materials division. In addition to recovering 3N to 4N gallium from scrap, the company has facilities to produce high-purity gallium for the U.S. and European markets. 21 United States St. George Mining operates a mine and processing plant near St. George, UT, to recover gallium contained in iron oxide minerals that remained at an abandoned copper mine. Gallium metal of 5N purity was produced at the 9,000-kg/yr plant until September 1987, when the plant was temporarily closed for repairs. In mid-1988, St. George Mining field for bankruptcy. Much of the gallium to be produced was expected to be shipped to Eagle- Picher's plant in Quapaw, OK, for refining to 6N to 7N purity. Eagle-Picher has a 3,000-kg/yr capacity to recover gallium from zinc residues generated at its Quapaw plant, but has not produced virgin gallium since 1982. However, the company does produce 4N, 5N, and 7N gallium metal from gallium concentrates and GaAs and GaP scrap. Sulzer Brothers Inc. plans to complete construction of a 15,000-kg/yr gallium extraction facility by the end of 1988. The plant, in Gramercy, LA, will obtain Bayer liquor from Kaiser Aluminum & Chemical Corp.'s alumina refinery at the same location, which uses bauxite from Jamaica as its feed source. The first 2 years' production is scheduled to be shipped to Europe in the form of a gallium chloride solution to be used in a solar neutrino capture experiment. After this commitment has been fulfilled, a decision will be made concerning the plant's future gallium production. Rhone-Poulenc plans to construct a 50,000-kg/yr gallium purification plant at Freeport, TX, by 1988. The plant is expected to use the 3N to 4N gallium recovered at the company's plant in Australia as feedstock. The 6N to 7N gallium metal produced at the refinery is expected to be used by the United States. Recapture Metals Inc. began operating a 4,000-kg/yr gallium recycling facility in Blanding, UT, in 1986. Although the company can produce gallium with a purity of 6N to 7N, most of its product is 3N to 4N gallium. HIGH-PURITY ARSENIC PRODUCTION Arsenic is recovered as arsenic trioxide in about 20 countries from the smelting or roasting of nonferrous metal ores or concentrates. Arsenic metal, which accounts for only about 3 pet of the world demand for arsenic, is produced by the reduction of arsenic trioxide. Commer- cial-grade arsenic metal, 99-pct-pure arsenic, is produced in only a few countries, and this grade accounts for the majority of arsenic metal production. High-purity arsenic, 4N purity or greater, for use in the semiconductor industry is produced by about 10 companies. Furukawa Co. Ltd. in Japan and Preussag in the Federal Republic of Germany are believed to be the world's largest producers, with reported capacities of 30,000 kg/yr and 15,000 kg/yr, respectively. Other high-purity arsenic producers include Cominco in Canada, Mitsubishi Metal and Rasa Industries in Japan, and Johnson Matthey Ltd. and MCP Electronic Materials Ltd. in the United Kingdom. GALLIUM ARSENIDE INGOT, WAFER, AND DEVICE MANUFACTURERS Table 9 lists companies involved in various phases of GaAs wafer and device manufacture. As is evident from the number of companies listed for these countries, most of the advanced GaAs manufacturing occurs in the United States and Japan. Some companies are fully integrated from GaAs ingot manufacture through device manufacture, while others make either wafers or devices. Table 9. - Gallium arsenide Ingot, wafer, and device manufacturers Country and company Ingot and wafer manufacture Epitaxy Device manufacture LEC HB LPE VPE MOCVD MBE Optoelectronic Analog Digital Canada: Cominco Electronic x Materials Ltd. France: Picogiga x The Philips Group x Thomson CSF x x Germany, Federal Ftepublic of: Siemens AG x x x x Wacker Chemitronic AG x x 22 Table 9. • Gallium arsenide Ingot, wafer, and device manufacturers— Continued Country and company Ingot and wafer manufacture Epitaxy Device manufacture LEC HB LPE VPE MOCVD ~MBE Optoelectronic Analog Digital Japan: Dowa Mining Co x Fujitsu Ltd x x Furukawa Co. Ltd x Hitatchi Cable Ltd x x x x Hitatchi Manufacturing Co. Ltd. . x x Iwaki Co. Ltd x Japan Victor Corp x Matsushita Electric Corp x x Mitsubishi Electric Corp x x Mitsubishi Metal Corp x x x Mitsubishi Monsanto Chemical x x x x Co. Ltd. NEC Corp x x Nippon Mining Co. Ltd x Oki Electric Industry Co. Ltd. ... x Sanyo Electric Co. Ltd x Sharp Corp x Shin-Etsu Semiconductor Corp. x Showa Denko K.K. . x Stanley Electric Co. Lid x Sumitomo Electric Industries Ltd. x x x x Sumitomo Metal Mining Co. Ltd. x x Toshiba Corp x x Sweden: Semitronics AB x United Kingdom: General Electric Co. (U.K.) .... x x x x x ICI Wafer Technology x MCP Electronic Materials Ltd. . . x Plessey PLC x x x United States: Airtron Div. of Litton Industries . x Anadigics Inc x x x Applied Solar Energy Corp x x AT&T Bell Laboratories x x x x Bertram Laboratories x Crystal Specialties Inc x x x x Epitronics Corp x x Ford Microelectronics Div. of x x Ford Motor Co. General Electric Co x x General Instrument Corp ■ x GigaBit Logic Inc Harris Microwave Semiconductor x Corp. Hewlett Packard Inc x x x x Honeywell Inc x x Hughes Aircraft Co x IBM Corp ITT Corp x Kopin Corp x Laser Diode Inc x M/A-Com Inc x McDonnell Douglas Corp x Morgan Semiconductor Div. of x x x Ethyl Corp. Motorola Inc x x Pacific Monolithics Inc x x Rockwell International Corp. . . . x x x x x Siemens Corp x x Spectrum Technology Corp. ... x Spire Corp x x Texas Instruments Inc x x x x TriQuint Semiconductor Inc. ... x x TRW Inc x x x x Varo Inc x x Vitesse Semiconductor Corp. . . x Westinghouse Electric Co x x x x x x X X X X X X X X X X XX X X X XX X X X 23 RESEARCH AND DEVELOPMENT Considerable research is being done concerning all phases of gallium extraction, GaAs material properties, and GaAs-based device manufacturing. Because GaAs IC manufacture is still in the developmental stage, much of the research activity centers on designing and manufac- turing devices. The Department of Defense sponsors a great deal of gallium research through the Defense Advanced Research Projects Agency (DARPA) and the National Aeronautics and Space Administration (NASA) as well as through the service branches' laboratories. Over the past few years, DARPA's focus in funding projects has been to increase the efficiency of processing GaAs devices. Although a variety of microwave and digital ICs have been fabricated from GaAs, many of these were prototype devices. Projects funded through DARPA were principally designed to increase the limited production of the prototype devices to full-scale manufacturing. Improving the manufacturing process may allow more complex ICs to be developed with increased radiation resistance and faster speed. By con- trast, NASA is principally investigating optoelectronic devices, particularly solar cells. NASA's main thrust is to increase the energy efficiency and reduce the cost of GaAs-based solar cells. In 1986, the Department of Defense announced that it would begin a $135 million program to develop MMICs for military electronic applications. The program, expected to begin in 1988, is called Mimic for Microwave/Millime- ter Wave Monolithic Integrated Circuit. Mimic would pro- vide funds for companies that are already involved in GaAs research to accelerate their activities. Most of the companies that are involved in the commercial GaAs market, both in optoelectronic devices and ICs, are involved in the development of devices that optimize the properties of GaAs. Among the new devices that are being developed are the high-electron-mobility transistor (HEMT), heteroj unction bipolar transistor (HBT), ballistic transistor, and quantum-well laser. HEMTs consist of an undoped GaAs substrate with a thin epitaxial layer of silicon-doped GaAlAs on top. When an electric current is passed through the HEMT, electrons from the impurity atoms in the GaAlAs layer fall into the GaAs layer, where they move very fast. HBTs operate in essentially the same manner, but the GaAlAs layer is more highly doped. Both HEMTs and HBTs could increase signal processing speed in MMICs and digital ICs. A ballistic transistor is basically a sandwich structure with two GaAlAs layers on both sides of an ultrathin GaAs layer. As in an HEMT device, electrons from the GaAlAs layer fall into the GaAs layer and pick up speed. But because the GaAs layer is so thin, electrons pass through the GaAs layer and into the second GaAlAs layer without slowing down. This enhanced electron movement could increase the speed of digital ICs and would allow MMICs to operate at high frequencies. The quantum-well laser is fabricated in the same way and with the same materials as the ballistic transistor, but instead of passing through the GaAs layer, electrons are trapped in this layer. By confining the charge carriers to this very small area, the chance is increased that they will recombine to emit light. Consequently, this structure increases the amount of light generated for a specific electrical signal (<5). Development of these new devices has been made possible with the advent of MOCVD and MBE, which are capable of depositing ultrathin layers on a substrate. With increased emphasis on developing new devices, demands have been placed on the GaAs substrate manufacturers to supply better quality and more uniform substrates. Consequently GaAs wafer manufacturers have been refining their crystal growth techniques to produce material with fewer defects, to improve the yield from gallium and arsenic metals to GaAs wafers, and to scale up production. At the same time, wafer manufacturers are trying to produce larger diameter wafers that ultimately could increase the yield from wafer to device. Companies involved in epitaxial growth are also working to improve properties such as the uniformity in the thickness and composition of the epitaxial layers. Recently metal-organic molecular beam epitaxy (MOMBE), also referred to as chemical beam epitaxy, has been developed to combine the advantages of MOCVD and MBE. These advantages include superior epitaxial layer thickness and uniformity, defect-free surfaces, the ability to grow layers on more than one wafer at a time, and the ability to introduce and control phosphorus atoms for optoelectronic device fabrication. MOMBE was introduced in early 1987. Work is also being done on combining GaAs with other materials to take advantage of the best qualities in each material. Prototypes of GaAs epitaxial layers grown on silicon substrates were recently produced, and sample quantities have been shipped to customers for testing. By using GaAs layers on a silicon wafer, the superior structural properties of silicon can be combined with the electrical and optical properties of GaAs. Larger, more durable wafers can be produced with light-emitting properties and increased radiation resistance. GaAs can be deposited by MOCVD or MBE over the entire silicon wafer, called blanket epitaxy, or islands of GaAs can be epitaxially deposited on the silicon wafer, called selective epitaxy. Wafers produced by blanket epitaxy could replace bulk GaAs wafers for GaAs MMICs and digital ICs. Wafers produced by selective epitaxy can combine silicon ICs with GaAs optoelectronic devices, GaAs MMICs, or GaAs digital ICs. Blanket epitaxial wafers would require less gallium than that consumed in the fabrication of bulk GaAs wafers, and selective epitaxial wafers would allow 24 GaAs to be used in areas in which its use is not currently feasible. In solar cells, where GaAs has not supplanted silicon to any great degree, epitaxial deposition of GaAs layers on germanium substrates may represent a hybrid substitute material for silicon. GaAs is fragile and can only be deposited in thick layers on a GaAs substrate. This puts GaAs at a disadvantage in comparison with silicon, which is sturdy and can be epitaxialry grown in thinner layers. Germanium substrates are stronger and less costly than GaAs substrates, and GaAs epitaxial layers can be grown thinner using MOCVD. Consequently the increased energy efficiency and radiation resistance of GaAs solar cells can be exploited, while reducing the total weight of GaAs-based solar cells. While providing the same power as silicon solar cells, GaAs-on-germanium solar cells can be made smaller, which allows a satellite to carry a larger payload. By continuing to ,push the limits of GaAs technology, researchers have also developed the optical equivalent of the transistor, a GaAs-based IC that controls light in the same manner a transistor controls electrical current. Thousands of alternating layers of GaAs and GaAlAs, each 40 atoms thick, are used in the construction of the IC. When a voltage is applied, the material becomes transparent, allowing a laser beam to shine through. A second, less powerful laser beam concentrates the electrical voltage in certain layers, which become opaque. Thus the second laser beam controls the transmission of the first laser beam. The outgoing light beam from one device can then be used as an input for a second device. Development of these devices could be a step in developing an optical computing device that would use light to transmit information rather than using electrical power. Basic research is being performed on the extraction of gallium from nontraditional source materials. The Bureau of Mines has investigated the extraction of gallium from phosphorus flue dust and low-grade domestic resources (7-8). Work is also being done by private firms to recover gallium from coal fly ash and phosphorus flue dust. LEGISLATION AND GOVERNMENT PROGRAMS Historically, gallium has not been impacted by legislative action, except for transportation requirements. In 1976, the U.S. Department of Transportation classified gallium as a hazardous material for purposes of transpor- tation. The amendment to the regulations prohibits trans- portation of liquid gallium aboard aircraft and specifies requirements for packaging solid gallium for aircraft trans- port and solid and liquid gallium for surface transport (9). Tariff rates for gallium and gallium oxide are shown in table 10. Under the proposed United States-Canada Free Trade Agreement, tariffs for gallium metal traded between the two countries will be removed on January 1, 1993. Table 10. - U.S. Import duties for gallium, January 1, 1989 Item Number Most favored nation (MFN) Gallium oxide. Gallium metal 8112.91.0000 2825.90.5000 3.7 pet ad valorem do Non-MFN 25.0 pet ad valorem. Do. STRATEGIC FACTORS Despite the fact that gallium is currently being used in some sophisticated military and satellite systems and is planned to be incorporated into additional systems, it has not been designated as a material to be added to the National Defense Stockpile. In 1986, Government and private agencies assessed the need to stockpile gallium, but because construction of additional gallium extraction plants is planned in North America, it was determined that in the event of a national emergency, gallium supplies would be adequate. If consumption increases dramatically over the next few years, it is likely that this assessment would be reevaluated. Although import dependence for gallium cannot be calculated according to the Bureau's formula, by comparing the U.S. production to the U.S. demand, it is apparent that the United States is highly dependent on imports to meet its needs. This import dependence is likely to continue because there is no planned construction of gallium extraction plants in the United States that would increase the commercial supply. Musto Explorations' existing extraction plant in Utah was operating at a significantly reduced capacity before its closure, and the gallium output of Sulzer Brothers plant under construction in Gramercy, LA will be shipped to Europe for at least 2 years. With the rapid technological progress, especially in GaAs IC development, the status of world supply and demand is changing dramatically. GaAs has advanced from a laboratory curiosity, a decade or so ago, to a material with distinct applications and almost no effective substitutes at present. Development of fiber optic telecommunications systems, the advent of sophisticated electronic military warfare, the widespread use of consumer electronics, and the need to process vast quantities of data in the shortest time possible have provided the impetus for implementing the large number 25 of GaAs research and development programs. By continuing to push the limits of GaAs technology, its applications have expanded. At the same time, continuing research into developing other "high-tech" materials, such as InP, superconductors, and organic polymer semicon- ductors, may yield materials with properties superior to those of GaAs. Development of these potential substitutes could radically alter the future of GaAs. REFERENCES 1. Zwiebel, K. Photovoltaic Cells. Chem. and Eng. News, v. 64, No. 27, July 7, 1986, pp. 34-48 2. Katrak, F. E, and J. C. Agarwal. Gallium: Long-Run Supply. J. Met., v. 33, No. 9, Sept. 1981, pp. 33-36. 3. Beja, M. Method of Extracting Gallium Oxide From Aluminous Substances. U.S. Pat. 2,574,008, Nov. 6, 1951. 4. de la Breteque, P. Method of Recovering Gallium From an Alkali Aluminate Lye. U.S. Pat. 2,793,179, May 21, 1957. 5. Frensley, W. R Gallium Arsenide Transistors. Sci. Am., v. 257, No. 2, Aug. 1987, pp. 80-87. 6. Brody, H. Ultrafast Chips at the Gate. High Technol., v. 6, No. 3, Mar. 1986, pp. 28-35. 7. Judd, J. C, M. P. Wardell, and C F. Davidson. Extraction of Gallium and Germanium From Domestic Resources. Paper in Light Metals 1988. Metall. Soc. AIME, 1987, pp. 857-862. 8. Neylan, D. L., C. P. Walters, and B. W. Haynes. Gallium Extraction From Phosphorus Flue Dust by a Sodium Carbonate Fusion- Water Leach Process. Paper in Recycle and Recovery of Secondary Metals. Metall. Soc. ATME, 1986, pp. 727-733. 9. Federal Register. V. 41, No. 172, Sept. 2, 1976, pp. 37114-37115. OTHER SOURCES U.S. Bureau of Mines publications: Gallium. Ch. in Mineral Commodity Summaries, annual. Gallium. Ch. in Minerals Yearbook, annual. Gallium. Ch. in Mineral Facts and Problems, quinquennial. U.S. GOVERNMENT PRINTING OFFICE 611-012/00.024 INT.-BU.OF MINES.PGH..PA. 28830 m O 33 ■o < > H m c c/> m o > I" GO c z m c/) "0 "0 O T> 00 C .S. Depa ureau of roduction ochrans .0. Box 1 ittsburgh, rtment Mines i & Dis Mill Ro 8070 ,PA 1 en o> ~ o ro q_ 5= x. « c =* O) O CD CD Oi o o m O c > r~ O "0 -o O 3 m O -< m 3D C 138 89 ? ^a ^. ♦*7C.« A '* **.. *?w .A 6- \*>CT V ^^v v^> h %*?&\* v^> v^Ev v^> W • ** ** •■ o, *'7Vi« A v % ^ .cat- \ •bv" » ^ ■ *°° .. v % -^*y x^s** V'*«^v °^^- / v #; — ^^ x* ->W%> "V ^ * v w ' / \ '-MR* ^ ^ V «V V^->" %*^%oo %;5®i-\/ V^%°° v^> •* ^o ;- ^o< • v ***** * • «? »&. « \>* m ^% f ." «> ^ • s ^\ --mms s\ -nm : . ♦♦""*- ^ •••»• «r » ^ q. * 7 ^f fl# .o° *<> % ^ 7, <** r ^d» JV r oV r <*& ^ '^HBL' J°+ #3 ^'* o° v^^v 1 S\ ' « • o HECKMAN BINDERY INC. HH MAY 89 !g^ N. MANCHESTER, *s=^ INDIANA 46962 ^ ^0 - * • ^ ^ , ^-o^ ^ **T;.-' o?' ^: ^v