3.4 Important Crystal Structures
53
Fig. 3.28 Schematic
molecular models of
orthorhombic- and
cubic-phase CsPbBr 3
perovskites with and
without PbCl 2 and Cl 2
doping. Adapted
from [232]
Fig. 3.29 Stability of
ABX 3 halide perovskites in
terms of octahedral factor
μ and tolerance factor t.
Red (black) dots indicate
stable (unstable)
compounds. The region of
unstable materials is shown
in grey. Adapted
from [231]
3.4.11 NiAs Structure
The NiAs structure (space group 194, P6 3 /mmc) (Fig. 3.30) is relevant for magnetic semiconductors,
such as MnAs, and also occurs in the formation of Ni/GaAs Schottky contacts [233]. The structure is
hexagonal. The arsenic atoms form a hcp structure and are trigonal prismatically configured with six
nearest metal atoms. The metal atoms form hcp planes and fill all octahedral holes of the As lattice.
For a cubic close packed, i.e. fcc, structure this would correspond to the rocksalt crystal. The stacking
is ABACABAC... (A: Ni, B,C: As).
3.4.12 Further Structures
There are many other crystal structures that have relevance for semiconductor materials. Among them
are the