Irradiation effect of 8 MeV protons on single-crystalline zinc oxide

Zinc oxide (ZnO) is a potential semiconductor to exhibit high radiation hardness since large threshold displacement energy for damage can be expected due to the small unit-cell volume and large bandgap energy. To study the radiation hardness, single-crystals of a ZnO thin film, a ZnO bulk, and a GaN bulk for reference were irradiated by 8 MeV protons at a wide range of the fluence from 2×10¹³ to 1×10¹⁷ p/cm². For the ZnO thin film, a rapid decrease of luminescence intensity followed by an increase of electrical resistance was observed at larger fluences than ~5×10¹⁴ p/cm². This threshold fluence was found to be much larger and larger than those of GaN and ZnO bulk crystals, respectively, indicating that ZnO is harder than GaN, and thin film is harder than the bulk material.