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Chapter One
1 Structural Properties
1.1 IONICITY
Details of ionicity [f.sub.i] are given in Adachi. Any given definition of ionicity is likely to be
imperfect. We present in Table 1.1 [f.sub.i] values for a number of group-IV, III-V and II-VI
semiconductors, including Be-based semiconductors and CdO. We have Phillips ionicity of
[f.sub.i] = 0 for all group-IV elemental semiconductors (diamond, Si, Ge and [alpha]-Sn) and [f.sub.i] > 0.9 for some alkali halides (NaCl, KCl, etc.).
Figure 1.1(a) plots [f.sub.i] versus x for [C.sub.x][Si.sub.1-x]. Note that [f.sub.i] = 0.177 for silicon carbide (SiC). This
means that the bond character of SiC resembles that of III-V or II-VI semiconductors
rather than of Si or diamond, so that its crystal structure must be zinc-blende, hexagonal or
rhombohedral. Similarly, an ordered alloy of [Si.sub.x][Ge.sub.1-x] may have a nonzero [f.sub.i] value near the ordered-phase composition x ~0.5. In fully disordered alloys ([C.sub.x ... read full excerpt from Properties of Semiconductor Alloys: Group-IV, III-V and II-VI Semiconductors (Wiley Series in Materials for Electronic & Optoelectronic Applications # ebook
