_applied sciences_  
_Article_  
**Effect of Selective Lateral Chromium Doping by RF Magnetron Sputtering on the Structural, and Opto-Electrical Properties of Nickel Oxide**  
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metal oxides. Doping of metal ions in transition metal-oxide thin films has recently been widely applied to tune the structural and optoelectronic properties [2; 3]. Adopting the appropriate metal dopant that can provide enormous conducting charges will alter the properties of NiO. NiO is a transition metal-oxide semiconductor which provides a platform with Ni\({}^{+3}\) and Ni\({}^{+2}\) ions for metal dopants to enhance the conductivity in fabricating devices [4]. Several scientists have made attempt to enhance the key properties of NiO by using different dopants, such as copper, iron, cobalt, manganese, lithium, and aluminum [2; 3; 4; 5; 6; 7; 8]. Doping transition metal elements into NiO offers the opportunity for fine tuning of the band gap along with tailoring of the structural and electrical properties. Cr is a typical transition metal element with an abundant electron shell structure. In addition, the ionic radius of trivalent Cr\({}^{+3}\) used a metal dopant (0.0615 nm) is very close to the ionic radius of Ni\({}^{+2}\) (0.0690 nm) and allows the replacement of nickel ions that leads to altered NiO properties.  
Several physical and chemical methods have been used to deposit NiO films. Examples of these methods include spray pyrolysis [9], radiofrequency (RF) magnetron sputtering [10; 11], DC magnetron sputtering [12], chemical vapor deposition [13], electron beam evaporation [14], and pulsed laser deposition [15]. The primary benefits of RF sputtering include the production of thin films that are pinhole-free, have uniform thickness, and can be deposited over a large surface area. In this process, the properties of thin films primarily depend on the substrate temperature, sputtering pressure, RF power, system geometry, and the distance between substrate and target [16; 17; 18; 19]. Most previous studies had focused on the doping of metal on NiO by sol-gel or chemical precipitation methods but reports on the deposition of chromium (Cr)-doped NiO by RF magnetron sputtering are rare. The purpose of this study is to create a compact, pinhole-free, and homogenous Cr doped NiO thin film using RF magnetron sputtering compared with others sol-gel or chemical precipitation methods. The concentration of Cr in the NiO was varied to investigate the optimum concentration for better film quality. This study is performed to investigate the structural, optical, and electrical properties of selective lateral doped Cr in NiO thin film by RF magnetron sputtering. For the first time, this approach (selective lateral doping) is employed to evaluate the optical, structural, and electrical properties of selective lateral Cr doped NiO thin film.