Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

TL;DR

This study investigates surface defect states in ZnO nanorods grown by chemical bath deposition, revealing transient photoluminescence behaviors linked to oxygen vacancies and environmental conditions, with implications for sensing and photovoltaic uses.

Contribution

It identifies specific deep level defects in ZnO nanorods and models their transient behavior influenced by environmental factors and surface band bending.

Findings

Deep level defects at 2.25 and 2.03 eV linked to oxygen vacancies.

Transient PL intensity decay times of 23 and 80 seconds in air.

Surface defect transient behavior correlates with atmospheric oxygen presence.

Abstract

Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies (V$_o$) were identified in ZnO nanorods (NRs) grown by low cost chemical bath deposition. A transient behaviour in the photoluminescence (PL) intensity of the two V$_o$ states was found to be sensitive to the ambient environment and to NR post-growth treatment. The largest transient was found in samples dried on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV exposure exhibited a transient behaviour in full agreement with the PL transient indicating a clear role of atmospheric O$_2$ on the surface defect states. A model for surface defect transient behaviour due to band bending with respect to the Fermi level is proposed. The results have implications for a variety of sensing and photovoltaic applications of ZnO NRs.