Efficient Auger Charge-Transfer Processes in ZnO

Abstract

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 chargetransfer process occurs between NBX and Fe 3þ . While the NBX dissociates, its hole is captured by an excited state of Fe 3þ 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.