Evaluation of oxygen vacancies in ZnO single crystals and powders by micro-Raman spectroscopy

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Abstract
Investigations of defects are important to understand the properties of zinc oxide (ZnO), especially oxygen vacancies, which are intrinsic defects that are easily generated during crystal growth or device processing. In this study, we evaluate the oxygen vacancies in ZnO single crystals and powders using micro-Raman spectroscopy. Reducing ZnO in a hydrogen atmosphere at 400–600°C for 30–240 min changes the amount of oxygen vacancies. Raman spectroscopy reveals a slight shift and a decrease in the E2(high) phonon mode, which is related to the oxide ion vibration. The peak position of the E2(high) mode shifts toward a lower frequency and the peak intensity decreases as the oxygen vacancies increase. This behavior can be explained by the existence of oxygen vacancies in ZnO. Because the E2(high) peak shift and the intensity are scaled in accordance with the amount of oxygen vacancies, these correlations offer a simple and useful probe to evaluate oxygen vacancies in ZnO.

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