Gallium arsenide. (GaAs). It is a compound of gallium and arsenic. It is an important semiconductor and is used to make devices such as microwave frequency integrated circuits, infrared emission diodes, laser diodes, and photovoltaic cells.
Summary
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- 1 Gallium
- 2 GaAs vs. Yes and ge
- 3 GaAs in high frequency technologies
- 4 Advantages
- 1 Disadvantages
- 5 Health effects of Gallium
- 6 Environmental effects of Gallium
- 7 Source
Gallium
Chemical element, symbol Ga, atomic number 31 and atomic weight 69.72. Lecoq de Boisbaudran discovered it in France in 1875 . It has a wide temperature range in the liquid state, and has been recommended for use in high-temperature thermometers and pressure gauges. In alloy with silver and tin, gallium adequately supplies amalgam in dental cures; It also serves to weld non-metallic materials. Gallium arsenide can be used in systems to transform mechanical motion into electrical impulses. Superconducting synthetic articles can be prepared by the manufacture of porous matrices of vanadium or tantalum impregnated with gallium hydride .
Gallium has shown excellent results as a semiconductor for use in rectifiers, transistors, photoconductors, light sources, laser or maser diodes, and refrigeration appliances.
Solid gallium appears bluish gray when exposed to the atmosphere. Liquid gallium is silvery white with a shiny reflective surface. Its freezing point is lower than that of any metal except for mercury (-39ºC or -38ºF) and cesium (28.5ºC or 83.3ºF).
The gallium is similar chemically to aluminum. It is amphoteric, but little more acidic than aluminum. The normal valence of gallium is 3+ and forms hydroxides, oxides, and salts. Gallium melts on contact with air when heated to 500ºC (930ºF). Reacts vigorously with boiling water, but slightly with room temperature water. Gallium salts are colorless; they are prepared directly from the metal , since the purification of the latter is simpler than that of its salts.
Gallium forms low melting point eutectic alloys with various metals, and intermetallic compounds with many others. All aluminum contains small amounts of gallium, as a harmless impurity, but large amounts of inter-granular penetration at 30 ° C cause catastrophic failure.
GaAs vs. Yes and ge
The physical and chemical properties of GaAs complicate its use in the manufacture of transistors as it is a binary compound with a lower thermal conductivity and a higher coefficient of thermal expansion (CET or CTE), while silicon and germanium are elemental semiconductors. In addition, failures in GaAs-based devices are more difficult to understand than those in silicon and can be more expensive, as they are much more recent to use. But comparing the relation quality and price, the added value of the GaAs compensates the manufacturing costs, in addition to the indicated markets are in continuous growth, which demand this technology that allows higher frequencies, which will help to reduce costs.
Gallium arsenide has been entering commercial markets since its technology began for the military and aerospace field.
It belongs to the semiconductor materials of the element group AIII-BV of the periodic table. The width of the band gap is greater than that of silicon or germanium. The mobility of electrons is also greater than that of silicon or germanium, and that of holes is similar to that of silicon .
Materials such as zinc, cadmium or copper are used to impurify it as type p since they introduce permitted levels in the range of 0.08 to 0.37 eV above the valence band of the GaAs. Donor materials are sulfur, selenium and the elements of group IV of the periodic table, in small concentration, if they replace gallium atoms.
GaAs is used for photoelectric cells, tunnel diodes, lasers, semiconductors, and MESFET transistors.
The GaAs has various circuit topologies and device types. The most dominant and commercially available is Direct Coupled FET Logic (DCFL) coupled, although Buffered FET Logic (BFL) and Schottky Diode FET Logic (SDFL) are also available.
GaAs in high frequency technologies
The effective mass of the electrical charge of the doped N-type GaAs is less than that of silicon of the same type, so the electrons in GaAs accelerate at higher speeds, taking less time to cross the transistor channel. This is very useful at high frequencies, since a higher maximum operating frequency will be achieved.
This possibility and need to work with circuits that allow operating at higher frequencies has its origin in the defense and space industries, in the use of radars, secure communications and sensors. Following development by federal programs, GaAs soon spread to new commercial markets, such as wireless local area networks (WLAN), personal communication systems (PCS), direct satellite transmission (DBS), transmission and reception by the consumer, global positioning systems (GPS) and mobile communications. All of these markets required working at high, unoccupied frequencies that could not be reached with silicon or germanium.
In addition, this has affected the semiconductor manufacturing philosophy, with statistical methods now being used to control uniformity and ensure the best possible quality without seriously affecting cost. All of this also enabled the creation of new digital transmission techniques at higher radio frequency power and low voltage / low voltage amplifiers to maximize the operating and standby time in battery powered devices.
Advantage
- The advantage of gallium arsenide over solar grade silicon is that it offers almost twice the efficiency. The great disadvantage, which explains its little use, is the price. To resolve this dilemma, engineers and researchers from the University of Illinois say they have achieved new methods of manufacturing low-cost thin films of gallium arsenide, which would allow the creation of devices that would replace silicon, increasing the efficiency of photovoltaic cells.
- Another announced achievement refers to increased efficiency. Gallium arsenide is usually deposited in a single thin layer on a small sheet. At the University of Illinois, multiple layers of material have been deposited on the wafers, obtaining a higher yield. Multiple layers remove limitations on the work area, which is very important in the case of solar cells, which require a wide coverage area to capture as much light as possible. Thus, its creators assure, a greater coverage area is achieved, generating more energy and lower cost.
- The use of arsenide in solar cells is not new. Here in Spain, it has also been used for years at the Solar Energy Institute of the Polytechnic University of Madrid, in multi-junction cells developed by Antonio Luque.
Disadvantages
- Devices made with GaAs can work at temperatures up to 450ºC. But despite these advantages, its technology poses some difficulties compared to that of silicon. For example, unlike silicon , there is no natural oxide that acts as a mask to produce simple elements of the MOS logic style.
Gallium health effects
Gallium is an element found in the body, but in very small amounts. For example, in a person with a mass of 70 kilos, there are 0.7 milligrams of gallium in her body. If this amount of gallium were condensed into a cube, the cube would only measure 0.49 millimeters per side. It has no proven benefits for bodily functions, and is most likely only present due to small amounts in the natural environment, in water, and in residues in vegetables or fruits. Some vitamins and commercially distributed waters are known to contain trace amounts of gallium of less than one part per million.
Pure gallium is not a dangerous contact substance for humans. It has been manipulated many times just for the simple pleasure of watching it melt away from the heat emitted by a human hand. However, it does leave stains on the hands. Even the radioactive component of the gallium citrate, gallium (67Ga) can be injected into the body and used for gallium scanning without harmful effects. Although not dangerous in small amounts, gallium should not be consumed on purpose in large doses. Some compounds of gallium They can be very dangerous indeed, however, high exposures to gallium (III) chloride can cause throat irritation, breathing difficulties, chest pain, and their vapors can cause very serious conditions such as pulmonary edema and partial paralysis.
Gallium environmental effects
A controversy with gallium involves nuclear weapons and pollution. Gallium is used to bond the mines together. However, when mines are cut and plutonium oxide powder forms, gallium remains in the plutonium. The plutonium is becomes unusable in fuel because the gallium is corrosive to several other elements. If galliumis removed, plutonium becomes useful again. The problem is that the process to remove gallium contributes to a large amount of pollution in the water with radioactive substances. Gallium is an ideal element to be used in mines, but pollution is destructive to Earth and to the health of its inhabitants. Even with efforts to remove water pollution, this would significantly increase the procedural costs of converting plutonium into a fuel (by about $ 200 million). Scientists are working on another method to clean up the plutonium , but it may take years for it to complete.
