Efficient Auger Charge-Transfer Processes in ZnO

Photoluminescence and magneto-optical measurements are performed on a line peaking at 3.354 eV (labeled as NBX) in electron-irradiated ZnO. Even though the energy position of the NBX line is close to that for bound excitons in ZnO, it has distinctively different magneto-optical properties. Photoelectron paramagnetic resonance measurements reveal a connection and a charge-transfer process involving NBX and Fe and Al centers. The experimental results are explained within a model which assumes that the NBX is a neutral donor bound exciton at a defect center located near a Fe impurity and an Auger-type charge-transfer process occurs between NBX and Fe3+. While the NBX dissociates, its hole is captured by an excited state of Fe3+ and the released energy is transferred to the NBX electron, which is excited to the conduction band and subsequently trapped by a substitutional Al-zn shallow donor.Funding Agencies|Swedish Energy Agency [43522-1]; Research Council of Norway; University of Oslo [251131]