On the role of Al in ultrasonically sprayed ZnO films

• Published in: Materials chemistry and physics 2017-01, Vol.185, p.137-142
• Main Authors: Kurtaran, S., Aldag, S., Ofofoglu, G., Akyuz, I., Atay, F.
• Format: Article
• Language: English
• Subjects: Aluminum; Aluminum oxide; Diffraction; Diffraction patterns; Doping; EDS; Electrical conductivity; Electrical properties; Electrical resistivity; Optical properties; Optoelectronics; Refractivity; Solubility; Spectroellipsometry; Spray pyrolysis; Studies; Surface properties; Thin films; Wurtzite; X-ray diffraction; Zinc oxide; Zinc oxides
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2016.10.016

In this work, Al incorporated ZnO films have been deposited by Ultrasonic Spray Pyrolysis technique. Behavior of Al element in the structure has been tried to be clarified by investigating the structural, optical, surface and electrical properties. Compositional analysis has been performed by EDX and Al contents in the coatings have been determined as 1.1, 2.8 and 3.1 at %. X-ray diffraction patterns have shown that all films are polycrystalline with hexagonal wurtzite structure and the dominant peak is (002) ZnO for films except the one containing the highest amount of Al. Above the Al content of 2.8 at %, appearance of new phases such as Al2O3 and ZnAl2O4 in XRD patterns refers a solubility limit at this doping rate. Thicknesses and optical constants (refractive index and extinction coefficient) have been determined by spectroscopic ellipsometry technique using Cauchy-Urbach model. Al doping above the solubility limit has caused ZnO films to have lower refractive index values. Also, AFM images have shown that surface morphologies of the films lose their spherical and granular texture and transform to a randomly clustered formation with sharper upper edges above the solubility limit. Transmittance and electrical resistivity measurements have shown that Al incorporation below solubility limit (1.1 and 2.8 at %) allows maintaining the transparency together with low resistivity values. These films have value to work on and may be promising materials for optoelectronic applications. •Resistivity was evaluated in terms of solubility limit using different mechanisms.•Spectroscopic ellipsometry was used to determine the optical constants.•Samples with 1.1–3.1 at %Al were obtained to express the behavior of Al.