Changes in the electrical transport of ZnO under visible light

TL;DR

This study investigates how visible light exposure affects the electrical impedance of ZnO crystals and thin films, revealing changes in relaxation times and identifying photo-active defects with specific activation energies.

Contribution

It provides new insights into the relaxation processes and defect states in ZnO under visible light, using impedance spectroscopy to analyze both single crystals and thin films.

Findings

ZnO shows significant impedance changes after light exposure.

Two relaxation times are identified, shorter in thin films.

Two photo-active defect states with activation energies between 0.8 and 1.1 eV are found.

Abstract

Complex impedance spectroscopy data in the frequency range 16Hz < f < 3 MHz at room temperature were acquired on pure ZnO single crystal and thin film. The measured impedance of the ZnO samples shows large changes with time after exposure to or covering them from visible light. At fixed times Cole-Cole-diagrams indicate the presence of a single relaxation process. A simple analysis of the impedance data allows us to obtain two main relaxation times. The behavior for both, ZnO crystal and thin film, is similar but the thin film shows shorter relaxation times. The analysis indicates the existence of two different photo-active defects with activation energies between ~0.8 eV and ~1.1 eV.