Group III-Nitride Semiconductors and Their Applications

Group III-nitrides are ionic compounds that involve elements from group III on the periodic table – that is to say, boron, aluminum, gallium, and indium – and the nitride ion. Like silicon, group III-nitrides are semiconductors, which makes them immensely useful in electronics. They are commonly used, for example, in the manufacture of transistors, light-emitting diodes or LEDs, and lasers. Well-known examples of their incorporation into diodes and lasers include Blu-ray discs and the Sony PlayStation 3.

One of the primary advantages of group III-nitride semiconductors has to do with heat capacity. Hence, group III-nitrides are far superior to silicon for use in components that must function at high temperatures. Silicon-based devices tend to deteriorate at temperatures above 100°C, or 212°F. By contrast, the melting points of group III-nitrides range from 1100°C to over 2500°C – which is to say, from 2012°F to over 4500°F. This difference is partially due to the fact that the heat capacities of group III-nitrides are orders of magnitude higher than the heat capacity of silicon: for example, compare 19.789 J/mol•K for silicon with 1.9967x10^7 J/mol•K for aluminum nitride. Because group III-nitride semiconductors are stable at extremely high temperatures, they are much more suited to the manufacture of high-power transistors than silicon.

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Group III-nitrides are amazingly versatile, and their applications extend beyond the realm of electronics. Hexagonal boron nitride, for instance, can serve as an effective lubricant at temperatures up to 900°C, or about 1650°F, and its function does not depend upon the presence of water or gas molecules. For this reason, hexagonal boron nitride can be used in space. Because of its chemical reactivity and conductivity, hexagonal boron nitride presents an excellent alternative to graphite in cosmetics and skin-care products, paints, and pencil lead. However, these products should not contain more than ten milligrams of boron nitride per cubic meter, as prolonged exposure to higher concentrations of boron nitride dust has been correlated with the onset of pneumoconiosis. Cubic boron nitride is preferable to diamond as an abrasive when machining steel, because, at sufficiently high temperatures, diamond will dissolve in iron and nickel, whereas boron nitride will not.

When the price of gallium nitride has dropped enough to make mass distribution feasible, gallium nitride may soon replace cavity magnetrons in microwave ovens. Military laboratories are already considering the use of gallium nitride in the construction of radar antennae with offensive capabilities such as jamming.

Group III-nitride semiconductors have applications in automobiles, aircraft, and wireless communication devices, and researchers are currently attempting to incorporate group III-nitride semiconductors into solar cells. Numerous advances have been made in the development of growth techniques for group-III nitride crystals, including the introduction of metalorganic chemical vapor deposition and plasma-induced molecular beam epitaxy, and these innovations have in turn enabled laboratories to optimize the electrochemical properties of group III-nitride semiconductors. As research on growth techniques continues, it is reasonable to expect that the number and range of industrial, commercial, and military applications for group III-nitride semiconductors will increase as well.

© Mark Ross 2004