Correlation between defect-related photoluminescence emission and anomalous Raman peaks in N-Al co-doped ZnO thin films

Abstract

The origins of defect-related photoluminescence (PL) and anomalous Raman peaks in N-doped ZnO are poorly understood. These features may be related to defects that control p-type conduction in N-doped and N-Al co-doped ZnO (AZO) films. In this study, we investigate the effects of introducing N2 gas during film deposition or a post-growth annealing process on crystallinity and defects in AZO films. A clear correlation between interstitial Zn (Zni)-related PL emissions and Raman features is found. X-ray diffraction and Hall results revealed that N was incorporated into AZO films deposited in the presence of N2 (N-doped AZO), whereas films annealed in N2 gas (N2-annealed AZO) had improved crystallinity with no substitution of N2 at O sites [(N2)O] or N at O sites (NO). The Raman scattering and PL spectra results indicated that Zni-related vibration and emission were dominant in the N-doped AZO films. X-ray photoelectron spectroscopy showed increases and decreases in the binding energies of Zn 2p and O 1s states in N2-annealed and N-doped AZO films, respectively. Together, these results demonstrate that the presence of Zni donor defects may be stabilized by the formation of small clusters and/or caused by the presence of NO acceptor defects, preventing p-type conduction in N-doped AZO films.