  The origin of nematicity, i.e., in-plane rotational symmetry breaking, and in
particular the relative role played by spontaneous unidirectional ordering of
spin, orbital, or charge degrees of freedom, is a challenging issue of
magnetism, unconventional superconductivity, and quantum Hall effect systems,
discussed in the context of doped semiconductor systems, such as
Ga$_{1-x}$Mn$_x$As, Cu$_x$Bi$_2$Se$_3$, and Ga(Al)As/Al$_x$Ga$_{1-x}$As quantum
wells, respectively. Here, guided by our experimental and theoretical results
for In$_{1-x}$Fe$_x$As, we demonstrate that spinodal phase separation at the
growth surface (that has a lower symmetry than the bulk) can lead to a quenched
nematic order of alloy components, which then governs low temperature magnetic
and magnetotransport properties, in particular the magnetoresistance anisotropy
whose theory for the $C_{2v}$ symmetry group is advanced here. These findings,
together with earlier data for Ga$_{1-x}$Mn$_x$As, show under which conditions
anisotropic chemical phase separation accounts for the magnitude of transition
temperature to a collective phase or merely breaks its rotational symmetry. We
address the question to what extent the directional distribution of impurities
or alloy components setting in during the growth may account for the observed
nematicity in other classes of correlated systems.
