  We study the interplay of fluctuations and superconductivity in
BaFe$_2$As$_2$ (Ba-122) compounds with Ba and Fe substituted by K ($p$ doping)
and Co ($n$ doping), respectively. To this end we measured electronic Raman
spectra as a function of polarisation and temperature. We observe gap
excitations and fluctuations for all doping levels studied. The response from
fluctuations is much stronger for Co substitution and, according to the
selection rules and the temperature dependence, originates from the exchange of
two critical spin fluctuations with characteristic wave vectors $(\pm\pi, 0)$
and $(0,\pm\pi)$. At 22\% K doping ($p=0.22$), we find the same selection rules
and spectral shape for the fluctuations but the intensity is smaller by a
factor of 5. Since there exists no nematic region above the orthorhombic
spin-density-wave (SDW) phase the identification of the fluctuations via the
temperature dependence is not possible. The gap excitations in the
superconducting state indicate strongly anisotropic near-nodal gaps for Co
substitution which make the observation of collective modes difficult. The
variation with doping of the spectral weights of the $A_{1g}$ and $B_{1g}$ gap
features does not support the influence of fluctuations on Cooper pairing.
Therefore, the observation of Bardasis-Schrieffer modes inside the nearly clean
gaps on the K-doped side remains the only experimental evidence for the
relevance of fluctuations for pairing.
