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

Influence of oxygen vacancies on surface charge potential and transportation properties of Al-doped ZnO nanostructures produced via atomic layer deposition
Khan, FirozBaek, Seong-HoKim, Jae Hyun
DGIST Authors
Baek, Seong-HoKim, Jae Hyun
Issued Date
Article Type
Al Doped ZnOAluminumAnnealingAtomic Force Microscopy (AFM)Atomic Layer Deposition (ALD)Charge PotentialsCharge TransportationDefect DensityDepositionDevicesDoping ConcentrationDoping ConcentrationElectrical PropertiesGel MethodKelvin Probe MethodOptical FilmsOxygenOxygen VacanciesPhotoelectron SpectroscopyPost Annealing TreatmentProbesPulsed Laser DepositionSemiconductor DopingSolar Cell ApplicationSurface ChargeSurface Charge PotentialTemperatureThin FilmsTransparentTransportation PropertiesX Ray Photoelectron SpectrometriesX Ray Photoelectron Spectroscopy (XPS)Zinc Oxide (ZnO) FilmsZinc Oxide (ZnO)
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 O2− species, corresponding to the oxygen in the ZnO lattice (OL); oxygen vacancies or defects (OV); and chemisorbed or dissociated (OC) oxygen species. In the case of the as-deposited films and films annealed under various atmospheres, a co-relationship between the OV and mobility (μ) can be determined. In the case of the N2-annealed film, the OV fraction is at its maximum value, while the other components are at their minimum values. Among the as-deposited films, the maximum OV fraction is obtained when a Al:Zn ratio (RAl/Zn) of 7% is used. When RAl/Zn = 7%, the μ value of the as-deposited AZO film is enhanced from 12.1 cm2V−1s−1 (RAl/Zn = 3%), to 18.5 cm2V−1s−1. It shows its potential application as photoanode. The Hall Effect and the XPS analysis of the film reviled a co-relationship between OV 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 N2-annealed AZO film with RAl/Zn = 3% (AZO-3-N2) exhibited the maximum negative potential (−115.79 mV); however, the film with RAl/Zn = 7% (AZO-7-N2) 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. © 2017 Elsevier B.V.
Elsevier Ltd
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