6.3 Band Structures of Selected Semiconductors
151
Fig. 6.19 Schematic energy levels in ABX 3 perovskites. Arrows indicate the shift of energy levels upon substitution of
atoms or small organic molecules. Adapted from [478]
(a)
(b)
Fig. 6.20 a Photoluminescence of CsPbX 3 nanocrystals of halide perovskites with various anions (colloidal solutions
in toluene under UV lamp (λ = 365 nm)). Adapted from [479]. b Position of conduction and valence band edges of
CsPbX 3 halide perovskites (relative to vacuum level at zero). Adapted from [480]
Fig. 6.21 Band gaps as a function of the lattice constant for various elemental, III–V and II–VI semiconductors. The
lattice constant of wurtzite semiconductors has been recalculated for a cubic cell (a 3
cubic =
√
3 a 2 c)
For the same lattice constant, the band gap increases with increasing ionicity, i.e. IV–IV→
III–V→II–VI→I–VII. A typical example is the sequence Ge→ GaAs→ZnSe→ CuBr, for which all
materials have almost the same lattice constant, and the band gaps increase 0.66 eV→1.42 eV→2.7 eV→
2.91 eV.