Stability and Optoelectronic Properties of Select Defects and Doping in Nickel Oxide

Nickel oxide (NiO) is a transparent conducting oxide (TCO) that shows

promise for novel semiconductor devices, such as next generation

non-volatile resistive RAM (RRAM), solar cells, and spintronics. Thus it is

of interest to study the intrinsic defects as isolated or forming complexes as

well as transition metals (TMs) and other dopants, namely Fe, Cu, Ag, and

C, in order to improve desired characteristics for these varied applications.

Hybrid density functional theory (DFT) based ab initio calculations were

used to study the energetics and stability of intrinsic, TM, and C defects

when introduced into rocksalt NiO. Results were obtained using hybrid

functional HSE06 to treat the exchange correlation within the pristine and

defective systems. Doped NiO systems were studied using supercells grown

along the [111] direction of 32 atoms to simulate anti-ferromagnetic

configurations. Stability was investigated through the calculation of the

formation energies of these systems in order to discern which are

energetically favorable. While Fe-doping is observed to shrink the band gap

and offer improved attributes for RRAM applications, Cu and Ag-doping

are observed to improve the optical character of NiO for possible use as a

hole transport layer in solar cell applications with potential for trap-state

formation depending on concentration. C-doping is observed to have

different effects depending on placement at a Ni (C Ni) or O (C O) site,

with anisotropy and deep trap states observed in the optical character for

C O.