High-temperature semiconductors

J. R. O Connor and J. Smiltens, eds., Silicon Carbide, A High Temperature Semiconductor, Pergamon Press, Inc., New York, 1960. 

High-power, high-frequency, and high-temperature semiconductor devices. P l... 

Chemical and phase purity are not always desirable. For example, H- and N-doped silicon carbide films behave as high temperature semiconductors, while silicon carbonitride glasses offer properties akin to glassy carbon with room temperature conductivities of 103 2 cm-118. Additional reasons for targeting materials that are not chemically or phase pure stem from the desire to control microstructural properties. 

SiC was made accidentally by E.G. Acheson in 1891. He recognized its abrasive power and named it carborundum [carbo(n) and (co)rundum (AI2O3)]. SiC is formed from coke and SiC>2 by sublimation in an electric furnace. Its hardness on the Mohs scale is 9.5, next to that of diamond (10). Carborundum has excellent abrasive power because of its hardness and the tendency to fracture to give sharp cutting edges. SiC is chemically stable, and is oxidized in air only above 1,000°C. (3-SiC is useful as a high-temperature semiconductor. SiC has been found as the mineral moissanite and in a meteorite found in Colorado. 

One of its two stable isotopes, 10B, is such a good absorber of neutrons that it is used in control rods in nuclear reactors. This property also makes it useful for construction of neutron detectors. Boron is used to make windows that are transparent to infrared radiation, for high-temperature semiconductors, and for electric generators of a thermoelectric type. 

The boron modifications are semiconductors. /3-rh. boron is a high-temperature semiconductor with a band gap of 1.5eV. The transition elements and some p elements (C, Si) form solid solutions in /3-rh. boron. In this manner, the electrical characteristics are changed (doping). The maximum solid solubility varies with solute and can be as high as 4 to 5 atomic percent. The well-known difficulties to prepare ultra-pure jS-rh. boron is partially due to the solid solutions that most of the elements form with boron. 

As mentioned, elemental silicon has the diamond structure. Silicon carbide, SiC, occurs in many crystalline forms, some based on the diamond structure and some on the wurtzite structure (see Figures 7-6 and 7-8(b)). It can be made from the elements at high temperature. Carborundum, one form of silicon carbide, is widely used as an abrasive, with a hardness nearly as great as diamond and a low chemical reactivity. SiC has now garnered interest as a high-temperature semiconductor. 

The first international conference on SiC was held in Boston, Massachusetts in 1959. Over 500 scientists attended the conference and 46 papers were presented. In 1968 and 1973, two other International Conferences were held, the last in Miami Beach. For almost ten years, the SiC effort in the USA, and around the world, went through another valley, except in the then USSR where the research effort remained fairly constant. This valley, or lack of interest, has been blamed on the lack of progress in crystal growth [4]. Nishino [5] and Powell [6] made a large contribution to the renewed interest in SiC with the development of the heteroepitaxial growth of SiC on Si. This effort was then duplicated by Sasaki et al [7], Liaw and Davis [8] and Harris et al [9]. These recent results have led to three SiC Workshops hosted by North Carolina State University (1986,1987,1988), four International SiC Conferences co-sponsored by Howard University and Santa Clara University, yearly SiC workshops in Japan, an international high temperature semiconductor conference, the formation of several SiC companies, SiC-based products, new SiC solid solutions, and an overall renewed interest in this material. 

Vasihev, A., Moritz, W., Filhpov, V, Bartholomaus, L.,Terentjev, A. and Gabusjan,T. (1998), High temperature semiconductor sensor for the detection of fluorine. Sensors and Actuators B, 49,133-8. 

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