150
6 Band Structure
6
4
2
0
-2
CuGaO 2
CuInO 2
CuAlO 2
Fig. 6.17 Band structures of CuAlO 2 , CuGaO 2 , and CuInO 2 , calculated with LDA (underestimating the absolute value
of the band gaps). The arrows denote the maximum of the valence band that has been set to zero energy for each material.
Adapted from [226]
Fig. 6.18 Calculated energy band structure of BaTiO 3 along the major symmetry directions. The Fermi level (E F ) is
set at zero energy. Adapted from [475]
discussed in [478]. The trends are summarized in Fig. 6.19. The band gap of halide perovskites can be
varied across the visible range, e.g. within the CsPb(Cl,Br,I) 3 the system (Fig. 6.20).
6.4 Systematics of Semiconductor Band Gaps
The trends with regard to the size of the band gap for elemental, III–V and II–VI semiconductors can
essentially be understood in terms of the bond strength and ionicity. In Fig. 6.21, the band gaps of many
important semiconductors are shown as a function of the lattice constant. For elemental semiconductors,
the band gap decreases with reduced bond strength, i.e. lattice constant (C→Si→Ge). A similar trend
exists both for the III–V and the II–VI semiconductors.