In this work, 1:1 complexes of the group 13 metal atoms with the group 15 hydrides are prepared with laser-ablation molecular beam techniques and studied with threshold photoionization and zero electron kinetic energy photoelectron spectroscopies and ab initio calculations. Ionization energies of the M-EH3 (M = Al, Ga, In; E = N, P, As) complexes increase in the order N < P less than or equal to As, whereas bond dissociation energies decrease down the group 15 hydrides. For a given hydride, the ionization and dissociation energies are different among the three metals, though the variation is smaller than that of the ligand effect. Ionization enhances the binding between the metal and ligand, and the enhancement is as large as three to five times.