  We measured the spin rectify effect and the inverse spin Hall effect in
Nb-doped SrTiO$_3$ by injecting the spins from ferromagnetic thin films to
SrTiO$_3$ using spin pumping. It was shown that the spin injection is increased
when the doping level is increased. However, the spin Hall angle decreases when
Nb occupies more than $\sim$2\% of the Ti sites, which is due to that beyond
this concentration, the electron contributed the spin Hall effect is from the
$d-$orbitals of Nb instead those from the Ti. Our work points to the importance
of orbital occupations in the (inverse) spin Hall effect. We may explore
controllable spin and charge interconversion in oxide spintronics.
