Influence of oxygen vacancies on surface charge potential and transportation properties of Al-doped ZnO nanostructures produced via atomic layer deposition

Abstract

Abstract High quality Al-doped ZnO (AZO) films are advantageous for many applications. Their properties can be tuned by controlling the doping concentration and intrinsic defect density. In this work, high-quality AZO films have been synthesized using the atomic layer deposition (ALD) technique. Throughout the doping cycle and post-annealing treatments under various atmospheres, the oxygen-related vacancies were controlled. The effect of oxygen vacancies on the charge transportation and surface potential were studied. The O 1s X-ray photoelectron spectrometry (XPS) spectra of the AZO film were deconvoluted into three components related to the O 2 − species, corresponding to the oxygen in the ZnO lattice ( O L ); oxygen vacancies or defects ( O V ); and chemisorbed or dissociated ( O C ) oxygen species. In the case of the as-deposited films and films annealed under various atmospheres, a co-relationship between the O V and mobility ( μ ) can be determined. In the case of the N 2 -annealed film, the O V fraction is at its maximum value, while the other components are at their minimum values. Among the as-deposited films, the maximum O V fraction is obtained when a Al:Zn ratio ( R Al/Zn ) of 7% is used. When R Al/Zn = 7%, the μ value of the as-deposited AZO film is enhanced from 12.1 cm 2 V −1 s −1 ( R Al/Zn = 3%), to 18.5 cm 2 V −1 s −1 . It shows its potential application as photoanode. The Hall Effect and the XPS analysis of the film reviled a co-relationship between O V and μ with the Al-doping concentration or post annealing atmosphere. Kelvin probe atomic force microscopy (KPFM) was used to evaluate the surface charge potentials of the films. The N 2 -annealed AZO film with R Al/Zn = 3% ( AZO-3-N 2 ) exhibited the maximum negative potential (−115.79 mV); however, the film with R Al/Zn = 7% ( AZO-7-N 2 ) exhibited the maximum positive potential (797.23 mV). Hence, the properties of these films may directly pertain to the bit readout signal and reliability of charge storage and memory applications.