The electronic band structure of GaAs in the SC16 structure along several lines of high symmetry is shown in Figure 4.33. The electronic structure of SC16 GaAs has been published previously but these were calculations based on empirical pseudopotentials where the experimental band gap of the zincblende structure is one of the fitted parameters. It clearly revealed an energy gap in the electronic states of SC16 GaAs of the same magnitude as that found in the zincblende and wurtzite structures. Furthermore, it was suggested that like-species bonds must be present in amorphous heteropolar semiconductors in order to account for the observed reduction in energy gap.
Figure 4.33: The band structure of GaAs in the SC16 structure shown along several lines of high symmetry in the simple cubic Brillouin zone.
The density of occupied states calculated here exhibits a close resemblance to that previously reported. However, as is evident from inspection of the band structure, the valence and conduction bands touch at the point of the Brillouin zone. In view of the well known inadequacies of density functional theory in determining the electronic excitation energies in solids this issue cannot be investigated further using these techniques although partial reduction of the energy gap may be due to the fact that both the bondlengths in the fully relaxed structure of SC16 GaAs are smaller than the ideal value found in the zincblende structure. This situation could have the effect of broadening the p-like region (approximately -5eV to 0eV) of the density of states.