Influence of pH on microstructure, optical features, surface resistivity and morphologies of CdO thin films chemically manufactured by a new approach

Abstract

In this work, the synthesis of nanostructured cadmium oxide (CdO) thin films by the low-cost chemical bath deposition method from a growth electrolyte containing both ammonia and EDTA was achieved for the first time. Then, the influence of the electrolyte pH varying between 10.0 and 11.5 on the composition, structure, optical features, surface resistivity, and surface morphology of resultant samples annealed at 400 degrees C was studied in detail. The compositional measurements performed by Energy-dispersive X-ray spectrometry demonstrated that the O/Cd ratio of the samples varied between 0.79 and 1.1 depending on the electrolyte pH. Structural results showed that the CdO samples have nanosized crystallites ranging from 27.4 to 31.3 nm and a preferential orientation along (111) and (200) planes. When the electrolyte pH was 11.0, the thickest and best crystallized CdO film was obtained . Electrical measurements performed using the four-probe method revealed that the CdO thin films manufactured at the electrolyte pH value of 11.0 (10.0) has the highest (lowest) surface resistivity of 16.040 (2.279) k Omega cm. There was also a good relationship between the surface resistivity and the surface roughness. All samples had a porous network morphology composed of nanoparticles. Furthermore, nanoparticles with an average size of similar to 70 nm became more distinct at the electrolyte pH of 11.0. The optical measurements showed that the CdO samples have a optical band gap ranging from 2.31 to 2.46 eV depending on the electrolyte pH.