Band gap density

When the stress (compressive) rises to a value approaching G/10 near the Debye temperature, motion of gliding dislocations tends to be replaced by the formation of phase transformation dislocations. The crystal structure then transforms to a new one of greater density. This occurs when the compressive stress (the hardness number) equals the energy band gap density (gap/molecular volume). 

Since chemical hardness is related to the gaps in the bonding energy spectra of covalent molecules and solids, the band gap density (Eg/Vm) may be substituted for it. When the shear moduli of the III-V compound crystals (isoelec-tronic with the Group IV elements) are plotted versus the gap density there is again a simple linear correlation. 

It is possible to identify particular spectral features in the modulated reflectivity spectra to band structure features. For example, in a direct band gap the joint density of states must resemble that of critical point. One of the first applications of the empirical pseudopotential method was to calculate reflectivity spectra for a given energy band. Differences between the calculated and measured reflectivity spectra could be assigned to errors in the energy band... 

Figure B3.2.5. The imaginary part of the dieleetrie fiinetion of GaAs, aeeording to tire AFC ELAPW-/c p method (solid eiirve) [195] and the experiment (dashed enrve) [196], To eorreet for the band gap underestimated by the loeal density approximation, the eonduetion bands have been shifted so that tlie 2 peaks agree in theory and experiment.

Solid solutions are very common among structurally related compounds. Just as metallic elements of similar structure and atomic properties form alloys, certain chemical compounds can be combined to produce derivative solid solutions, which may permit realization of properties not found in either of the precursors. The combinations of binary compounds with common anion or common cation element, such as the isovalent alloys of IV-VI, III-V, II-VI, or I-VII members, are of considerable scientific and technological interest as their solid-state properties (e.g., electric and optical such as type of conductivity, current carrier density, band gap) modulate regularly over a wide range through variations in composition. A general descriptive scheme for such alloys is as follows [41]. 

Table 2. Surface density (0 ), direct band gap energy (Egd), and number of next nearest neighbors (N ) on WO -ZrOi calcined at 1073 K.

Hamada, N. and Ohnishi, S. (1986) Self-interaction correction to the local-density approximation in the calculation of the energy band gaps of semiconductors based on the full-potential linearized augmented-plane-wave method, Phys. Rev., B34,9042-9044. 

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