  The nature of dark matter is still an open problem, but there is evidence
that a large part of the dark matter in the universe is non-baryonic,
non-luminous and non-relativistic and hypothetical Weakly Interacting Massive
Particles (WIMPs) are candidates that satisfy all of the above criteria. In
order to minimize the ambiguities in the identification of WIMPs' interactions
in their search, in more experiments, two distinct quantities are
simultaneously measured: the ionization and phonon or light from scintillation
signals. Silicon and germanium crystals are used in some experiments. In this
paper we discuss the production of defects in semiconductors due to WIMP
interactions and estimate their contribution in the energy balance. This
phenomenon is present at all temperatures, is important in the range of keV
energies, but is not taken into consideration in the usual analysis of
experimental signals and could introduce errors in identification for WIMPs.
