  Neutrinoless double beta decay would be a key to understanding the nature of
neutrino masses. The next generation of High Purity Germanium experiments will
have to be operated with a background rate of better than 10^-5 counts/(kg y
keV) in the region of interest around the Q value of the decay. Therefore, so
far irrelevant sources of background have to be considered. The metalization of
the surface of germanium detectors is in general done with aluminum. The
background from the decays of 22Na, 26Al, 226Ra and 228Th introduced by this
metalization is discussed. It is shown that only a special selection of
aluminum can keep these background contributions acceptable.
