## 4 Conclusions  
The crystal quality of Cr-doped NiO significantly worsened with the increase in doping time. The lattice constant of the Cr-NiO thin films also increased from 4.185 A to 4.250 A as the doping time was increased from 0 s to 80 s. This finding may be attributed to the film grains being strained at high doping levels. The microstrain and dislocation density increased at high doping times due to the stacking defect of films increases considerably with Cr doping. These parameters are the leading causes of the dislocation network in the Cr-NiO films. The increasing microstrain and dislocation density indicated the poor film quality at high doping times. The conductivity of the Cr-doped NiO increased with doping time, and the highest conductivity (8.73 \(\times\) 10\({}^{-2}\) Scm\({}^{-1}\)) and lowest resistance (11 \(\Omega\)-cm) were found at the doping time of 80 s. The highest carrier mobility (33.60 cm\({}^{2}\)/V\(\cdot\)s) was  
Figure 7: EDS mapping for (**a**) Ni (**b**) Cr and (**c**) EDS data for Cr doped NiO thin film.  
observed at a doping time of 40 s. Optical studies showed that the optical transmittance of the undoped NiO was approximately 84.92% within the visible region, but gradually decreased to ~68% as the doping time was increased from 0 s to 80 s. This phenomenon may have been caused by the increase in the Cr content in the NiO thin films. When the doping time was increased from 0 s to 80 s, the direct bandgap of Cr-doped NiO was reduced from 3.43 eV to 3.28 eV, and the Urbach energy of the Cr-NiO films increased from 181 meV to 458 meV. The highest Urbach energy was observed at a doping time of 80 s. This result indicated that the crystallinity became poorer, and the degree of defect increased with doping time.  
M.S.J.: Writing--original draft; K.S. ([PERSON]): Conceptualization, formal analysis; H.M.: Writing--review & editing; T.N.: Methodology; K.A.: Writing--review & editing; H.I.A.: validation & visualization; M.S.: editing & visualization; K.S. ([PERSON]): Project administration & funding acquisition; N.A.: Supervision; M.A.: Supervision & Writing--review & editing. All authors have read and agreed to the published version of the manuscript.  
The research is supported by Universiti Kebangsaan Malaysia, Malaysia for financial support through Long-term Research Grant Scheme (LRGS/1/2019/UKM-UKM/6/1) and Taif University Researchers Supporting Project Number (TURSP-2020/241). The authors duly acknowledge the publication fee related support from iRMC, Universiti Tenaga National, Malaysia.  
Data will be made available by the corresponding author upon reasonable request.  
We acknowledge the Universiti Kebangsaan Malaysia, Malaysia for financial support through Long-term Research Grant Scheme (LRGS/1/2019/UKM-UKM/6/1). The authors duly acknowledge the publication fee-related support from iRMC, Universiti Tenaga National, Malaysia. The authors would also like to acknowledge the support from Taif University Researchers Supporting Project Number (TURSP-2020/241), Taif University, Taif, Saudi Arabia. The study was also partially supported by the Bangabandhu Science and Technology Fellowship Trust (BSTFT) under the Ministry of Science and Technology, Bangladesh.  
The authors declare no conflict of interest.