William III

Dutch Willem Alexander Paul Frederik Lodewijk

(born Feb. 19, 1817, Brussels, Belg.—died Nov. 23, 1890, Apeldoorn, Neth.) King of The Netherlands and grand duke of Luxembourg (1849–90). Son of William II, he succeeded to the throne on his father's death in 1849. Opposed to the liberal constitution of 1848, he adopted an anti-Catholic posture and from 1862 to 1868 was able to rule through the cabinet. He tried to sell his sovereignty over Luxembourg to France (1867) but yielded to Prussia's demand that the area be independent. Following this crisis, his influence over parliament declined. On his death, he was succeeded by his daughter, Wilhelmina.

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orig. Dauferi

(born 1027, Benevento, principality of Benevento—died Sept. 16, 1087, Montecassino, principality of Capua; beatified July 23, 1887; feast day September 16) Pope (1086–87). As abbot of Monte Cassino from 1058, he promoted manuscript illumination, established a school of mosaic, and reconstructed the abbey. He served as papal vicar in southern Italy, negotiating peace between the Normans and the papacy. He was proclaimed pope against his will and was soon driven from Rome by supporters of Emperor Henry IV and the antipope Clement III. In 1087, after briefly retiring to his abbey, Victor resumed his papal authority and promoted the reforms of his predecessor, Pope Gregory VII. After sending an army to defeat the Saracens at Tunis (1087), he called a synod at Benevento and excommunicated Clement. He fell ill and returned to Monte Cassino, where he died.

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Italian Vittorio Emanuele

(born Nov. 11, 1869, Naples, Italy—died Dec. 28, 1947, Alexandria, Egypt) King of Italy (1900–46). Son of Umberto I, he came suddenly to the throne on his father's assassination (1900). He accepted a Liberal cabinet and readily agreed to Italy's war against Turkey (1911–12) and entry into World War I. After the war, he failed to prevent the rise of Benito Mussolini and the fascist seizure of power, which turned him into a figurehead sovereign. In 1943, after disastrous Italian military losses and the Allied invasion of Sicily, he had Mussolini arrested and replaced by Pietro Badoglio as premier. In 1944 he relinquished power to his son Umberto and, in an unsuccessful attempt to preserve the monarchy, abdicated in Umberto's favour in 1946 (see Umberto II). When the Italian republic was declared in 1946, father and son went into exile.

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(born April 30, 1961, Chicago, Ill., U.S.) U.S. basketball player, coach, and executive. He led Indiana University to a national collegiate h1 in 1981. As a guard for the Detroit Pistons (1981–94), he amassed 9,061 career assists and helped the team win two NBA championships (1989, 1990); he is regarded as one of the greatest point guards of all time. He subsequently worked as general manager for the Toronto Raptors and New York Knicks and coached the Indiana Pacers.

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(born Dec. 24, 1761, Constantinople, Ottoman Empire—died July 29, 1808, Constantinople) Ottoman sultan (r. 1789–1807). He inherited the throne during a losing war with Austria and Russia (1787–92), with whom he later signed treaties. Napoleon I's invasion of Egypt in 1798 drove him into an alliance with Britain and Russia, but, impressed with Napoleon's successes, he switched sides in 1806. At home he attempted tax and land reform and established a European-style military corps, but, unable to enforce his reforms in the face of mutinies among the Janissaries and other units, he rescinded them. He was promptly overthrown and was strangled on the orders of his successor, Mustafa IV.

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orig. John Stewart, earl of Carrick

(born circa 1337—died April 4, 1406, Rothesay, Bute, Scot.) King of Scotland (1390–1406). After having ruled in the name of his father, Robert II, from 1384 to 1388, he assumed the throne in his own right on his father's death. Physically disabled by a kick from a horse in 1388, he was never the real ruler of Scotland. His brother Robert, earl of Fife, later duke of Albany, governed during Robert II's last years and continued to govern throughout Robert III's reign, except for three years when Robert III's eldest son, David, duke of Rothesay, took his place. Robert III's other son became James I.

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(born Oct. 2, 1452, Fotheringhay Castle, Northamptonshire, Eng.—died Aug. 22, 1485, Bosworth, Leicestershire) Last Yorkist king of England. He was made duke of Gloucester in 1461 after his brother Edward of York had deposed the weak Lancastrian king Henry VI and assumed power as Edward IV. Richard and Edward were driven into exile in 1470 but returned and defeated the Lancastrians in 1471. On Edward's death (1483), Richard became protector for Edward's son, the 12-year-old King Edward V, but he usurped the throne and confined Edward and his little brother to the Tower of London, where they were murdered. Henry Tudor (later Henry VII) raised an army against Richard, who was defeated and killed at the Battle of Bosworth Field. Later Tudor histories and William Shakespeare's play Richard III painted Richard as a monster and were gross caricatures motivated by the new dynasty's need to denigrate its predecessor.

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Spanish Felipe

(born April 14, 1578, Madrid, Spain—died March 31, 1621, Madrid) King of Spain and of Portugal (1598–1621). The son of Philip II, he was an indifferent ruler and allowed royal favourites to govern in his place. From 1609 his government continued the policy of expelling the Moriscos (Christians of Moorish ancestry), which caused serious economic problems. The huge sums he spent on court entertainments exacerbated Spain's growing economic problems.

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Russian Pyotr Fyodorovich orig. Karl Peter Ulrich, duke von Holstein-Gottorp

(born Feb. 21, 1728, Kiel, Holstein-Gottorp—died July 18, 1762, Ropsha, near St. Petersburg, Russia) Tsar of Russia (1762). Grandson of Peter I, the young duke was brought to Russia by his aunt Elizabeth when she became empress (1741). Proclaimed the heir to the Russian throne, he was unpopular at court for his pro-Prussian attitude. After he succeeded Elizabeth (1762), he reversed her foreign policy, making peace with Prussia and withdrawing from the Seven Years' War. He offended the Orthodox church by trying to force it to adopt Lutheran practices. After six months he was forced to abdicate by a group of nobles, in collusion with his own wife, Catherine (later Catherine II), and Count Grigory Orlov, and was murdered while in the conspirators' custody.

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orig. Alessandro Farnese

(born Feb. 29, 1468, Canino, Papal States—died Nov. 10, 1549, Rome) Pope (1534–49). The son of a noble Tuscan family, he was made a cardinal-deacon in 1493 and served as bishop in Parma and Ostia before being named dean of the College of Cardinals by Pope Leo X. Ordained a priest in 1519, he was unanimously elected pope in 1534. Though loose in morals in earlier years (he had three sons and a daughter), he became an efficient promoter of reform, convening the Council of Trent in 1545 and initiating the Counter-Reformation. He also supported the newly founded Jesuits and was a patron of the arts, the last in the tradition of the Renaissance popes.

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(born July 980—died Jan. 23, 1002, near Viterbo, Italy) German king (983–1002) and emperor (996–1002). He was elected German king at age 3, and his mother and grandmother served as regents until he came of age in 994. He went to Rome to put down a rebellion (996) and installed his cousin as Gregory V, the first German pope. After returning in 997 to quell another revolt, he made Rome the centre of his empire. He saw himself as leader of world Christianity and hoped to revive the glory of ancient Rome in a universal Christian state. When Rome rebelled against him (1001), he requested help from Bavaria but died before it arrived.

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or Louis-Napoléon orig. Charles-Louis-Napoléon Bonaparte

(born April 20, 1808, Paris, France—died Jan. 9, 1873, Chislehurst, Kent, Eng.) Emperor of France (1852–70). The nephew of Napoleon, he spent his youth in exile in Switzerland and Germany (1815–30). With the death in 1832 of Napoleon's son, Napoléon-François-Charles-Joseph Bonaparte, duke von Reichstadt, he became the claimant to the French throne. After an abortive coup d'état, he was exiled by King Louis-Philippe to the U.S. After another attempted coup (1840), he was arrested, tried, and imprisoned. He escaped to England (1846) and returned to Paris (1848), where he was elected to the national assembly. He evoked the legend of Napoleon to win the popular vote as president of the Second Republic. Attempting to expand his power, he staged a coup in 1851 and made himself dictator; in 1852, as Napoleon III, he became emperor of the Second Empire. Seeking to reestablish French power, he led France into the Crimean War and helped negotiate the treaty at the Congress of Paris (1856). He sided with Sicily against Austria (1859) and was victorious at the Battle of Solferino. He aided Italy in achieving unity and annexed Savoy and Nice (1860). He promoted liberalized policies within France, which enjoyed prosperity during much of his reign. In the 1860s he gradually introduced political liberalization. He expected material rewards from his “Latin empire” after installing Maximilian as emperor of Mexico (1864–67) but was disappointed. He kept France neutral in the Austro-Prussian War (1866), but in 1870 Otto von Bismarck contrived to involve France in the disastrous Franco-Prussian War. After leading his troops to defeat in the Battle of Sedan (September 1870), Napoleon surrendered and was deposed as emperor.

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orig. Mikhai Khristodolou Mouskos

(born Aug. 13, 1913, Pano Panayia, Cyprus—died Aug. 3, 1977, Nicosia) Archbishop and primate of the Orthodox Church of Cyprus and president of Cyprus (1959–77). Son of a poor shepherd, he was ordained in 1946; he became bishop in 1948 and archbishop in 1950. A supporter of Cyprus's union with Greece, opposing both independence and partition, he negotiated with the British governor of Cyprus (1955–56) but was arrested for sedition and exiled. In 1959 he accepted independence for Cyprus and was elected president, with a Turkish vice president. Twice reelected, he fled Cyprus following an attempted coup by the Greek Cypriot National Guard (1974). Despite a subsequent invasion by Turkey and the establishment of a separate Turkish Cypriot state in the north, he resisted partition of the country.

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orig. Léopold-Philippe-Charles-Albert-Meinrad-Hubertus-Marie-Miguel

(born Nov. 3, 1901, Brussels, Belg.—died Sept. 25, 1983, Brussels) King of the Belgians (1934–51). He succeeded his father, Albert I, and favoured an independent foreign policy but not strict neutrality. In World War II he assumed command of the Belgian army, but he surrendered his encircled forces 18 days after the German invasion in May 1940. The Belgian government repudiated his decision to surrender and remain with his forces rather than join the government-in-exile in London. Under house arrest through the war, he later went to Switzerland (1945–50) to await resolution of the controversy. Though 58percnt of voters voted for his return to the throne, he abdicated in 1951 in favour of his son Baudouin.

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known as Leo the Isaurian

(born circa 675, Germanicia, Commagene, Syria—died June 18, 742, Constantinople) Byzantine emperor (717–41), founder of the Isaurian dynasty. A high-ranking military commander, he seized the throne with the help of Arab armies who hoped to subjugate the Byzantine Empire. He then successfully defended Constantinople against the Arabs (717–718). Having crowned his son Constantine V coemperor (720), Leo used his son's marriage to cement an alliance with the Khazars. Victory over the Arabs at Akroïnos (740) was crucial in preventing their conquest of Asia Minor. Leo issued an important legal code, the Ecloga (726). His policy of iconoclasm (730), which banned the use of sacred images in churches, engendered a century of conflict within the empire and further strained relations with the pope in Rome.

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(born circa 1837, Mushu, Bechuanaland—died Feb. 21, 1923, Serowe) South African chief. In 1885 he had Bechuanaland (now Botswana) declared a protectorate of the British Empire. He lent reinforcements to the British expedition that crushed Lobengula in 1893. His grandson Sir Seretse Khama (1921–80) was the first president of independent Botswana (r. 1966–80).

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(born May 1452—died June 11, 1488, near Stirling, Stirling, Scot.) King of Scotland (1460–88). He succeeded his father, James II. Unlike the latter, he was unable to restore strong central government after his long minority. A weak monarch, he was confronted with two major rebellions. He evidently offended his nobles by his interest in the arts and by taking artists for his favourites. In 1488 two powerful border families raised a rebellion and won to their cause his son, the future James IV; James III was captured and killed at age 36.

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known as Ivan the Great

(born Jan. 22, 1440, Moscow—died Oct. 27, 1505, Moscow) Grand prince of Moscow (1462–1505). Determined to enlarge the territory he inherited from his father, Ivan led successful military campaigns against the Tatars in the south (1458) and east (1467–69). He subdued Novgorod (1478) and gained control of most of the remainder of Great Russia by 1485. He also renounced Moscow's subjection to the khan of the Golden Horde (1480) and won a final victory over the khan's sons in 1502. Stripping the boyars of much of their authority, he laid the administrative foundations of a centralized Russian state. Ivan IV the Terrible was his grandson.

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orig. Lothar of Segni

(born 1160/61, Gavignano Castle, Campagna di Roma, Papal States—died July 16, 1216, Perugia) Pope (1198–1216). Innocent, who was trained in both theology and law, brought the medieval papacy to the height of its prestige and power. He crowned Otto IV as Holy Roman emperor, but Otto's determination to unite Germany and Sicily angered him, and in 1212 he gave his support to the Hohenstaufen candidate, Frederick II. After Innocent excommunicated King John of England for refusing to recognize Stephen Langton as archbishop of Canterbury, John was obliged to submit and to declare England a fief of the Holy See (1213). Innocent launched the Fourth Crusade, which captured Constantinople, and the Albigensian Crusade, which attempted to suppress heresy in southern France. He approved the Mendicant orders founded by St. Dominic and St. Francis of Assisi, and he convoked the fourth Lateran Council, which promulgated the doctrine of transubstantiation and endorsed annual confession for all Christians.

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orig. Cencio Savelli

(born Rome—died March 18, 1227, Rome) Pope (1216–27). He extended Innocent III's policies on church reform and the recovery of the Holy Land, proclaiming a Crusade to regain Jerusalem in 1216 (see Crusades). He crowned Frederick II as Holy Roman emperor (1220) but threatened to excommunicate him if he failed to join the Crusade. Honorius also undertook a Crusade against the Moors in Spain (1218) and settled the Barons' War in England (1223). He continued the Albigensian Crusade against the heretics of southern France. He approved the Dominican, Franciscan, and Carmelite orders and authorized the first official book of canon law.

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German Heinrich

(born Oct. 28, 1017—died Oct. 5, 1056, Pfalz Bodfeld, near Goslar, Saxony) Duke of Bavaria (as Henry VI, 1027–41), duke of Swabia (as Henry I, 1038–45), German king (1039–56), and emperor (1046–56). He gained sovereignty over Bohemia and Moravia and arranged the election of Pope Clement II, who crowned him emperor. The last emperor to dominate the papacy, Henry appointed three more popes in succeeding years. He championed the church reform advocated by the monasteries of Cluny and Gorze. He was nearly deposed in a revolt (1054–55), and in his later years his influence faltered in northeastern Germany, Hungary, southern Italy, and Lorraine.

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orig. George William Frederick

(born June 4, 1738, London, Eng.—died Jan. 29, 1820, Windsor Castle, near London) King of Great Britain and Ireland (1760–1820); also elector (1760–1814) and king (1814–20) of Hanover. The grandson of George II, he ascended the throne during the Seven Years' War. His chief minister, Lord Bute, forced William Pitt's resignation and caused intrigue rather than stability within the government. Bute resigned in 1763, but George's political overtures to others were snubbed, until Lord North became prime minister in 1770. England was in financial distress caused by the war, and George supported attempts to raise funds through taxation of the American colonies, which led to the American Revolution. With North, he was blamed for prolonging the war and losing the colonies. He reasserted his power when North and Charles James Fox planned to take control of the East India Company; he forced them to resign and reaffirmed his control through a new “patriotic” prime minister, William Pitt, the Younger. George supported him until the war with Revolutionary France (1793) and fears of related uprisings in Ireland caused Pitt to propose political emancipation of the Roman Catholics. George's vehement opposition led to Pitt's resignation in 1801. In 1811 George's ill health and a return of the madness that had afflicted him for short periods earlier in his life caused Parliament to enact the regency of his son, the future George IV.

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German Friedrich Wilhelm

(born Aug. 3, 1770, Potsdam, Prussia—died June 7, 1840, Berlin) King of Prussia (1797–1840). The son of Frederick William II, he pursued a policy of neutrality in the early years of the Napoleonic Wars, which accelerated the decline of Prussia's prestige. Prussia joined the third coalition against France in 1806 and suffered crushing defeat at the Battles of Jena and Auerstedt. Defeat convinced the king of the need to make decisive changes. He allowed Prussian statesmen such as Karl August, prince von Hardenberg, and Karl, imperial baron vom Stein, to make domestic reforms, though the state remained absolutist. The Congress of Vienna confirmed Prussia's acquisition of Westphalia and much of Saxony, but the last 25 years of the king's reign brought a downward trend in Prussia's fortunes.

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German Friedrich

(born Sept. 21, 1415, Innsbruck, Austria—died Aug. 19, 1493, Linz) Holy Roman emperor from 1452 and king of Germany (as Frederick IV) from 1440. By 1439 he was the senior member of the Habsburg dynasty, and he united the Austrian holdings of two rival branches of the dynasty (partitioned in 1379), helping to lay the foundations for the greatness of the house of Habsburg in European affairs. His greatest achievement was marrying his son Maximilian (later Maximilian I) to Mary, daughter of Charles the Bold, which gave the house of Habsburg a large part of Burgundy and made the Austrians a European power. Frederick was the last emperor to be crowned in Rome by a pope.

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(born July 13, 1608, Graz, Inner Austria—died April 2, 1657, Vienna) Holy Roman emperor (1637–57), archduke of Austria (1621–57), king of Hungary (1625–57) and king of Bohemia (1627–57). Denied command of the Habsburg armies in the Thirty Years' War, Ferdinand conspired to overthrow Gen. Albrecht W.E. von Wallenstein, whom he replaced as commander (1634–35). His leadership of the so-called peace party at the imperial court led to the Peace of Prague in 1635. As emperor from 1637, he refused to allow religious freedom in his own domains, but he compromised with Europe's Protestant powers and agreed to the Peace of Westphalia, ending 30 years of religious strife in central Europe.

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known as Edward of Windsor

(born Nov. 13, 1312, Windsor, Berkshire, Eng.—died June 21, 1377, Sheen, Surrey) King of England (1327–77). His mother, Isabella of France, deposed his father, Edward II, and crowned the 15-year-old Edward in his place. Isabella and her lover, Roger de Mortimer, governed in Edward's name for four years and persuaded him to grant the Scots their independence (1328). After having Mortimer executed in 1330, Edward became the sole ruler of England. By asserting his right to the French crown, he began the Hundred Years' War. He instituted the Order of the Garter in 1342. He defeated the French at the Battle of Crécy (1346) and captured Calais (1347), though lack of funds forced him to sign a truce. The Black Death hit England in 1348, but fighting continued. The Scots surrendered to Edward in 1356, and the same year his son Edward the Black Prince won a major victory for the English at the Battle of Poitiers. In 1360 Edward gave up his claim to the French crown in return for Aquitaine. The war later resumed when Charles V repudiated the Treaty of Calais; Edward lost Aquitaine, and he signed a new truce in 1375. In his later years he fell under the influence of his greedy mistress, Alice Perrers, and his son John of Gaunt.

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(born 1093—died Feb. 15, 1152, Bamberg, Ger.) German king (1138–52), the first of the Hohenstaufen dynasty. Nephew of Emperor Henry V of Germany, he revolted when he was passed over as heir by the electors, and he was crowned antiking at Nürnberg (1127) and king of Italy (1128). Returning to Germany in 1132, he fought the German king Lothar II until 1135, when Conrad submitted and was pardoned. He became king when Lothar died, quelling resistance in Bavaria and Saxony. Conrad set out for Palestine on the Second Crusade (1147) and visited Constantinople (1148), where he cemented an alliance with Manuel I Comnenus. Unable to visit Rome, he never received the imperial crown.

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(died 219 BC) Agiad Spartan king (r. 235–222). Seeking to institute social reforms, in 227 he canceled debts, redistributed land, and restored the training of youth. He abolished the ephors and introduced the patronomoi (board of six elders). His early attempts to weaken the Achaean League (from 229) were successful, but in 222 his army fell at Sellasia to a Macedonian force summoned by the league. He fled to Egypt, where he was imprisoned but escaped (219); having failed to stir up revolt in Alexandria, he committed suicide.

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(born Aug. 12, 1503, Gottorp, Schleswig—died Jan. 1, 1559, Kolding, Den.) King of Denmark and Norway (1534–59). Son of King Frederick I, he assumed control of the kingdom after winning a civil war known as the Count's War. He arrested the Catholic bishops who had opposed him and organized the Diet of Copenhagen (1536), which confiscated episcopal property and established the state Lutheran church. By forming close ties between the church and the crown, he laid the foundation for the absolutist Danish monarchy of the 17th century.

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known as Charles the Fat

(born 839, Bavaria? [Germany]—died Jan. 13, 888, Neidingen) Frankish king and emperor (881–87). The great-grandson of Charlemagne, he inherited the kingdoms of Swabia (876) and Italy (879). Charles was crowned emperor by the pope in 881. He gained control of the eastern and western Frankish kingdoms on the deaths of their rulers, and by 885 he had reunited all of Charlemagne's empire except Provence. Chronically ill, he failed to attack the Saracens and used tribute to buy off Viking invaders. His nephew Arnulf led an uprising against him in 887, and his fall marked the final disintegration of the empire of Charlemagne.

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known as Casimir the Great Polish Kazimierz Weilki

(born April 30, 1310, Kujavia, Pol.—died Nov. 5, 1370) King of Poland (1333–70). He was the son of Władysław I, who revived the Polish kingship, and he continued his father's quest to make Poland a power in central Europe. He crafted treaties with Hungary, Bohemia, and the Teutonic Order and acquired Red Russia and Masovia by diplomacy. Casimir also arranged a series of dynastic alliances that tied Poland to many royal European families. He codified Teutonic law, gave new towns self-government under the Magdeburg Law, and founded the University of Kraków.

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Polish August Fryderyk

(born Oct. 17, 1696, Dresden, Saxony—died Oct. 5, 1763, Dresden) King of Poland and elector of Saxony (as Frederick Augustus II), whose reign (1733–63) marked a great period of disorder within Poland. He cared more for pleasure than affairs of state and left the administration of Saxony and Poland to his chief adviser, Heinrich von Brühl (1700–1763), and the powerful Czartoryski family. He gave Saxon support to Austria in the War of the Austrian Succession and the Seven Years' War.

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known as Antiochus the Great

(born 242—died 187 BC, near Susa, Iran) Seleucid king of the Syrian empire (223–187 BC). After quelling a rebellion by Achaeus, his governor in Asia Minor (213), Antiochus marched east to India (212–205). He forged a peaceful alliance with Armenia and forcible ones with Parthia and Bactria, stilling resistance to his campaign. After the death of Ptolemy IV, Antiochus and Philip V of Macedonia divided most of his empire, Antiochus taking the southern and eastern lands, including Palestine (circa 202). He then marched against Egypt, concluding a peace in 195, through which he acquired southern Syria and Ptolemy's territories in Asia Minor. Rome grew angry with Antiochus after he admitted Hannibal of Carthage to his court; when Antiochus took a force to defend the Aetolians against Rome, Rome struck against him, eventually defeating him at Magnesia (189). He gave up lands in Europe and western Asia Minor but kept Syria, Mesopotamia, and western Iran. He was murdered while exacting much-needed tribute near Susa.

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(born Sept. 2, 1241—died March 18/19, 1286, near Kinghorn, Fife, Scot.) King of Scotland (1249–86). Son of Alexander II, he came to the throne at age 7. In 1251 he was married to Margaret, daughter of England's King Henry III, who sought to gain control over Scotland. In 1255 Alexander was seized by a pro-English party in Scotland; in 1257 the anti-English party gained control of the government until he came of age (1262). In 1263 he repulsed a Norwegian invasion, and in 1266 he acquired the Hebrides and the Isle of Man from Norway. His reign was later viewed as a golden age by Scots caught up in the long conflict with England.

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}} Gallium arsenide (GaAs) is a compound of two elements, gallium and arsenic. It is an important semiconductor and is used to make devices such as microwave frequency integrated circuits (ie, MMICs), infrared light-emitting diodes, laser diodes and solar cells.

Preparation and chemistry

Gallium arsenide can be prepared from the elements and a number of industrial processes use this, for example:

• the crystal growth using a horizontal zone furnace (Bridgman-Stockbarger technique) where Ga and Arsenic vapour react and deposit on a seed crystal at the cooler end of the furnace.
• LEC (liquid encapsulated Czochralski) growth

Alternative methods for producing films of GaAs include :

• VPE reaction of gaseous gallium metal and arsenic trichloride

2Ga + 2AsCl₃ → 2GaAs + 3Cl₂

• MOCVD reaction of trimethylgallium and arsine:

Ga(CH₃)₃ + AsH₃ → GaAs + CH₄

Wet etching of GaAs industrially uses an oxidising agent e.g. hydrogen peroxide or bromine water, and the same strategy has been described in a patent relating to processing scrap components containing GaAs where the Ga³⁺ is complexed with a hydroxamic acid, "HAe.g.:

GaAs + H₂O₂ + "HA" → "GaA" complex + H₃AsO₄ + 4H₂O

Oxidation of GaAs occurs in air and degrades performance of the semiconductor, the surface can be passivated by depositing a cubic gallium(II) sulfide layer using a tert-butyl gallium sulfide compound such as (^tBuGaS)₇

Applications

GaAs advantages

GaAs has some electronic properties which are superior to those of silicon. It has a higher saturated electron velocity and higher electron mobility, allowing transistors made from it to function at frequencies in excess of 250 GHz. Also, GaAs devices generate less noise than silicon devices when operated at high frequencies. They can also be operated at higher power levels than the equivalent silicon device because they have higher breakdown voltages. These properties recommend GaAs circuitry in mobile phones, satellite communications, microwave point-to-point links, and some radar systems. It is used in the manufacture of Gunn diodes for generation of microwaves.

Another advantage of GaAs is that it has a direct band gap, which means that it can be used to emit light efficiently. Silicon has an indirect bandgap and so is very poor at emitting light. (Nonetheless, recent advances may make silicon LEDs and lasers possible).

Due to its high switching speed, GaAs would seem to be ideal for computer applications, and for some time in the 1980s many thought that the microelectronics market would switch from silicon to GaAs. The first attempted changes were implemented by the supercomputer vendors Cray Computer Corporation, Convex, and Alliant in an attempt to stay ahead of the ever-improving CMOS microprocessor. Cray eventually built one GaAs-based machine in the early 1990s, the Cray-3, but the effort was not adequately capitalized, and the company filed for bankruptcy in 1995.

Complex layered structures of gallium arsenide in combination with aluminium arsenide (AlAs) or the alloy Al_xGa_1-xAs can be grown using molecular beam epitaxy (MBE) or using metalorganic vapour phase epitaxy (MOVPE). Because GaAs and AlAs have almost the same lattice constant, the layers have very little induced strain, which allows them to be grown almost arbitrarily thick.

Silicon's advantages

Silicon has three major advantages over GaAs for integrated circuit manufacture. First, silicon is abundant and cheap to process. Si is highly abundant in the Earth's crust, in the form of silicate minerals. The economy of scale available to the silicon industry has also reduced the adoption of GaAs.

The second major advantage of Si is the existence of silicon dioxide—one of the best insulators. Silicon dioxide can easily be incorporated onto silicon circuits, and such layers are adherent to the underlying Si. GaAs does not form a stable adherent insulating layer.

The third, and perhaps most important, advantage of silicon is that it possesses a much higher hole mobility. This high mobility allows the fabrication of higher-speed P-channel field effect transistors, which are required for CMOS logic. Because they lack a fast CMOS structure, GaAs logic circuits have much higher power consumption, which has made them unable to compete with silicon logic circuits.

Solar cells and detectors

Another important application of GaAs is for high efficiency solar cells. In 1970, the first GaAs heterostructure solar cells were created by Zhores Alferov and his team in the USSR. In the early 1980s, the efficiency of the best GaAs solar cells surpassed that of silicon solar cells, and in the 1990s GaAs solar cells took over from silicon as the cell type most commonly used for Photovoltaic arrays for satellite applications. Later, dual- and triple-junction solar cells based on GaAs with germanium and indium gallium phosphide layers were developed as the basis of a triple junction solar cell which held a record efficiency of over 32% and can operate also with light as concentrated as 2,000 suns. This kind of solar cell powers the rovers Spirit and Opportunity, which are exploring Mars' surface. Also many solar cars utilize GaAs in solar arrays.

Complex designs of Al_xGa_1-xAs-GaAs devices can be sensitive to infrared radiation (QWIP).

GaAs diodes can be used for the detection of x-rays.

Light emission devices

GaAs has been used to produce (near-infrared) laser diodes since the early 1960s.

Single crystals of gallium arsenide can be manufactured by the Bridgeman technique, as the Czochralski process is difficult for this material due to its mechanical properties. However, an encapsulated Czochralski method is used to produce ultra-high purity GaAs for semi-insulators.

GaAs is often used a substrate material for the epitaxial growth of other III-V semiconductors including: InGaAs and GaInNAs.

Safety

The toxicological properties of gallium arsenide have not been thoroughly investigated. On one hand, due to its arsenic content, it is considered highly toxic and carcinogenic. On the other hand, the crystal is stable enough that ingested pieces may be passed with negligible absorption by the body. When ground into very fine particles, such as in wafer-polishing processes, the high surface area enables more reaction with water releasing some arsine and/or dissolved arsenic. The environment, health and safety aspects of gallium arsenide sources (such as trimethylgallium and arsine) and industrial hygiene monitoring studies of metalorganic precursors have been reported.. California lists gallium arsenide as a carcinogen

See also

• Electronics
• Field effect transistor
• Heterostructure emitter bipolar transistor
• Integrated circuit
• Semiconductor
• Semiconductor devices
• solar cell
• magnetic semiconductor
• Photomixing

Related materials

• Aluminium arsenide
• Aluminium gallium arsenide
• Arsine
• Gallium antimonide
• Gallium arsenide phosphide
• Gallium phosphide
• Gallium nitride
• Indium arsenide
• Indium gallium arsenide
• Indium phosphide
• MOVPE
• Trimethylgallium

References

External links

• Case Studies in Environmental Medicine: Arsenic Toxicity
• Extensive site on the physical properties of Gallium arsenide
• Facts and figures on processing Gallium Arsenide