Electrical characterization of as-grown and particle irradiated n-type bulk ZnO

Nickel oxide/ZnO structures and Ru Schottky barrier diodes (SBDs) on ZnO were used as rectifying contacts to study defects in ZnO by deep level transient spectroscopy DLTS. In the as-grown bulk Zn DLTS measurements revealed the presence of three major electron traps with levels at 0.04 eV, 0.12 eV and 0.29 eV below the conduction band, respectively. The shallowest of these levels may be the same level previously detected by Hall measurements, EPR and ENDOR, shown to be hydrogen-related. 5.4 MeV alpha particle bombardment introduced two additional deep electron traps at 0.54 eV and 0.93 eV below the conduction band, respectively. We speculate that one of these may be the oxygen vacancy, V_O, predicted by theory to be a deep donor level. From these particle radiation studies we found that ZnO is about two orders of magnitude more radiation hard than GaN for identical radiation conditions.