Optoelectronic Properties Induced by Carbon Doping in NiO

Nickel oxide (NiO) is a transparent conducting oxide (TCO) that has shown promise for novel semiconductor devices, particularly in next generation resistive random access memory (RRAM) and solar cell applications [1]. Carbon doping in NiO has also been shown to offer active sites for water dissociation due to adsorption of H by unsaturated Ni bonds behaving effectively as a catalyst [2]. Recently, experiments have indicated improved electrochemical properties of NiO grown upon graphene. Moreover, the presence of C in NiO may be used to tune the mechanical and electronic properties, due to the potential for diffusion of C across the graphene heterojunction interface. However, due to a large density of O vacancies and the presence of Ni vacancy induced acceptor states [3,4], device efficiency is limited. Through doping with C, NiO properties may be tuned to improved optoelectronic efficiency [4]. In this work, we show the results of hybrid density functional theory calculations on the structural, electronic, and optical properties of pure and C-doped NiO. C doping at the Ni site (CNi) results in a reduction of the pure NiO electronic band gap as well as a red shift in all primary optical properties. C doping at the O site (CO) also reduces the electronic band gap but inter-band gap states emerge which are comprised of deep O 2p electronic states. An anisotropy exists in the optical response where adsorption onset is red shifted and the long wavelength limit refractive index (n(λ → ∞, E → 0)) is increased. Formation energy calculations show that CNi is favored over CO but both may exist depending on the ambient growth conditions, where CNi can help to modify the electronic band edges while CO can introduce deep trap states in the electronic band gap.

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[2] T. Kou, et al., Nat. Commun. 11 (2020) 1–10.

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[4] K.O. Ukoba, et al., Int. J. Photoenergy. (2018) 1–8.