Amorphous indium-zinc-oxide films were deposited in the "transition region" by reactive sputtering using an In-Zn alloy target with a specially designed double feedback system. The cathode voltage showed a V-and circle-shaped curve as a function of O-2 gas flow in the transition region, which differs from the S-shaped curve in Berg's model for reactive sputtering depositions. In-situ analyses with a quadrupole mass spectrometer combined with an energy analyzer revealed that the negative ions O-, O-2(-), InO-, and InO2-, with high kinetic energies corresponding to the cathode voltage, were generated at the partially oxidized target surface. Furthermore the positive ions O+, Ar+, In+, and Zn+ with rather low kinetic energies (around 10 eV) were confirmed to be generated by the charge exchange of sputtered neutral O, Ar, In and Zn atoms, respectively. (C) 2013 Elsevier B.V. All rights reserved.