# Why is the Ionization Energy of Germanium less than that of Silicon?

I've read that in the 13th period, Ga has higher I.E. than Al because of the filling of the d-orbitals in Ga.

The text said they have low penetration,hence they don't shield well and the effective nuclear charge on the valence electrons increases.

But, shouldn't Germanium have a higher I.E. than Silicon by the same logic? Why doesn't it?

Also, why does Indium again have lower I.E. even though it has filled d-orbitals.