Control of the structural, electrical and optical properties of spin coated NiO films by varying precursor molarity

In this work, Nickel oxide (NiO) films were coated over Si (100) substrates at different precursor molarities (0.1–0.9 M) using sol-gel spin coating technique. The structural, morphological, electrical and optical properties of the films were investigated. X-ray diffraction and field-emission scanning electron microscopy (FESEM) results indicated that the crystalline quality of NiO films was improved with increasing the precursor molarity. All NiO films are composed of well-defined nanograins as confirmed by FESEM analysis. The average size of these nanograins was increased from ~20 to ~ 36 nm as the precursor molarity was increased from 0.1 to 0.9 M. The electrical measurements indicated that all NiO films exhibited p-type conductivity. The carrier concentration was decreased from 14.30 × 10¹⁶ to 0.0098 × 10¹⁶ cm⁻³ with the increase of molarity from 0.1 M to 0.9 M, whereas the resistivity and mobility were increased from 36.92 to 7840 Ω.cm and from 1.26 to 9.96 cm² v⁻¹ s⁻¹, respectively. The energy band gap of the films was decreased from 3.85 to 3.31 eV upon increasing the molarity from 0.1 to 0.9 M. Based on our findings, NiO film prepared at 0.9 M displayed the best properties and hence it is a good candidate in various applications.