  In the layered iron-based superconductor YFe2Ge2, a high Sommerfeld ratio of
~100 mJ/molK^2 and a T^(3/2) temperature dependence of the electrical
resistivity at low temperature T indicate strong electronic correlations and
point towards an unconventional pairing state. We have investigated the role of
composition and annealing conditions in optimizing the growth of high-quality
YFe2Ge2. Our findings confirm that bulk superconductivity is observed in
samples with disorder scattering rates less than 2 k_B T_c/hbar. Fe deficiency
on the Fe site is identified as the dominant source of disorder, which can be
minimised by precipitating from a slightly iron-rich melt, following by
annealing.
