Comprehensive Characterization of Nitrogen-Doped Zinc Oxide Thin Films Produced by Metalorganic Chemical Vapour Deposition (MOCVD)

Abstract

This study aimed to produce nitrogen doped zinc oxide thin films from a cheap and easily reproducible precursor. This was with a view to provide an effective link for the production of nitrogen doped zinc oxide thin films which will be suitable for various technological applications. The raw materials for the precursor were zinc acetate and ammonium acetate. The precursor was produced from the two compounds in proportions (ammonium acetate to zinc acetate) of 1:9 (10%), 2:8 (20%), 3:7 (30%) and 4:6 (40%), and designated as Samples B1, B2, B3 and B4 respectively. The formulations were processed powder-dry and each sample was cracked in MOCVD deposition chamber to deposit ZnO thin films on glass substrates successfully at 420°C. The working pressure was atmospheric while compressed air was used as the carrier gas with a flow rate of 2.5 dm3/min. The ZnO thin films deposited were characterized to get their optical, structural, compositional and electrical properties and surface morphology. The optical characterization showed that all the deposited thin films were over 80% transparent to the visible spectrum. Sample B1 had peak transmittance of 95.0% at 785nm wavelength, B2 had 96.7% peak at 970nm, B3 had 99.0% peak at 1040nm, and B4 had 93% peak at 1090nm. The optical measurements also gave the energy bandgap of 3.27eV for Samples B2 and B3, and 3.31eV for Samples B1 and B4. The x-ray diffraction analyses showed that the deposited thin films were amorphous, and gave poorly defined peaks at \(2\theta=32.9°\) for Samples B1, B2 and B4 and at \(2\theta=30.6°\) for Sample B3. RBS measurements gave a fairly constant (average) ratio for the three identified elements in the thin films (zinc : oxygen : nitrogen) as 4.4 : 3.7 : 1. Thicknesses obtained through the RBS were 14.43\(\mu\)m for B1, 58.72\(\mu\)m for B2, 52.28\(\mu\)m for B3, and 36.09\(\mu\)m for B4. The sheet resistivity was on the high side, but lowered a bit sharply from B1 to B2, gradually from B2 to B3, and much more sharply from B3 to B4. The values were 1.53 x 109 \(\Omega\)/sq. for B1, 1.10 x 109 \(\Omega\)/sq. for B2, 1.00 x 109 \(\Omega\)/sq. for B3, and 8.00 x 107 \(\Omega\)/sq. for B4. The micrographs showed extensively aligned clusters of grains with some (nitrogen) gas bubbles on some of the surfaces. This study concluded that the precursor produced could be used to deposit doped zinc oxide thin films which could also be useful in solid state device fabrication, gas sensors and anti-reflectors.