Materials for High-Temperature Semiconductor Devices (1995) / Chapter Skim
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State of the Art of Wide Bandgap Materials
State of the Art of Wide Bandgap Materials
Pages 15-30
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From page 15... ...
This chapter is not a comprehensive examination of all the properties of the different materials, but does examine closely those properties related to hightemperature operation. The intrinsic properties of the wide bandgap materials versus those of the more common silicon and gallium arsenide (GaAs)
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Methods of Fabrication Bulk Growth The commercial potential of SiC semiconductor technology has been enhanced by recent significant progress in the growth of large single-crystal SiC boules.
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In 1955, Lely developed a laboratory sublimation process for growing crystals that were much purer (Lely, 19551. In the Lely process, a hollow cavity was formed inside a charge of polycrystalline SiC.
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The basic elements of the modified sublimation process are shown in Figure 2-6, which is a schematic diagram of the configuration used by Westinghouse. Nucleation takes place on a SiC seed crystal located at one end of a cylindrical cavity.
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While conventional semiconductors are grown at approximately two-thirds of their melting temperatures, these temperatures are not practical with wide bandgap materials. For this reason, the substrate temperature cannot be used to assure that all components of the activation energy have been exceeded.
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A typical SiC CVD growth chamber, shown in Figure 2-7, is similar to chambers used for silicon (Powell et al., 19871. The quartz chamber is water-cooled because growth temperatures are generally higher than those used for silicon epitaxy.
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basal plane (Tairov and Tsvetkov, 19831. The research team of Matsunami at Kyoto University discovered that the CVD growth temperature required for producing good-quality 6H-SiC epilayers on 6H-SiC substrates could be reduced from about 1750 °C to about 1450 °C if the growth surface was off-axis by a few degrees from the (0001)
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From page 24... ...
Excellent epitaxial films of or-SiC polytypes can now be grown on ~x-SiC substrates. Both e-type and p-type films with net carrier concentrations from 10~4 cm:3 to greater than 10~9 cm~3 can be routinely achieved.
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by Nichia, the successful growth of better samples, and the accumulation of more precise data (Strife and Morkoc, 1992; Choyke and Linkov, 1993; Lin et al., 1994; Morkoc et al., 1994~. Properties The most intriguing aspect of the large bandgap nitrides (i.e., A1N, GaN, and InN)
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From page 26... ...
Indium nitride exhibits a direct bandgap of 1.9 eV and an indirect bandgap only slightly higher. Its thermal conductivity and most other properties have not yet been definitively ascertained.
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~ .; ~ 1 1 1 1 . _ 3 I_ _ _ ~ _ 1 _ _ 3 3 /`Conduction ~ \ Band ~ 2 \: b ~/ 16~ N3/ /Valence \ ,~ Band <\_ _ ; - ~ 3 '4= l ~ ~ 1 K r M X r A k FIGURE 2-9 Band structure of hexagonal and cubic modifications of The nitride materials, like diamond, are very difficult to etch with liquid etchants.
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. Methods of Synthesis and Characterization Aside from the high-pressure, high-temperature synthesized boules of diamond, virtually all diamond films are grown by plasma-assisted methods in the presence of an abundance of atomic hydrogen.
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From page 29... ...
For every 104 hydrogen atoms removed from the diamond surface, only one Is replaced by a carbonaceous radical; the remainder are replaced by another hydrogen. The growth process is thus slow and relatively inefficient, although DC arc jets and combustion jets have grown diamond at rates exceeding 100 micron/in.
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The full width at half maximum Raman signature has been correlated with the thermal conductivity of diamond. In polycrystalline diamond films, a full width at half maximum Raman signature of 3.2 cm~~ generally ensures that the thermal conductivity (in the direction of growth)
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