Incorporation and Compensatory Doping Processes of Cu into ZnO Nanowires Investigated at the Local Scale

The Cu compensatory doping of ZnO nanowires is of great interest to face the challenge arising from the detrimental screening of the piezoelectric potential generated under mechanical solicitations. However, the incorporation processes of Cu into ZnO nanowires are largely unknown. Here, they are investigated locally by combining mass spectrometry and optical spectroscopy with X‐Ray linear dichroism using synchrotron radiation. By varying the Cu(NO₃)₂/Zn(NO₃)₂ concentration ratio from 0 to 10% in a chemical bath kept at high pH, it is shown that the amount of Cu incorporated into ZnO nanowires varies from around 4.5 × 10¹⁶ to 3.6 × 10¹⁸ at cm⁻³. However, only 15% of the incorporated Cu forms Cu_Zn‐related defects, while the remaining Cu lies on the surfaces of ZnO nanowires. Importantly, thermal annealing under O₂ atmosphere is found to electrically activate the incorporated Cu, resulting in the formation of Cu_Zn‐related defect complexes involving nearby V_Zn, the structured green emission band with a strong phonon coupling, and the increase in the electrical resistivity. These findings shed light on the local environment of Cu incorporated into ZnO nanowires and the required conditions for electrically activating the compensatory doping, as an important outcome for enhanced piezoelectric nanogenerators and stress/strain sensors.