Crystallographic Characteristics and p-Type to n-Type Transition in Epitaxial NiO Thin Film

Abstract

We were able to systematically control crystallographic characteristics and electrical properties of nickel oxide epitaxial thin films integrated with cubic yttria-stabilized zirconia (c-YSZ)-buffered silicon(001) substrates. The NiO epilayers were grown under several oxygen partial pressures by pulsed laser deposition. The out-of-plane orientation of the NiO layers showed an interesting behavior where it changed from ⟨111⟩ at lower pressures (7 × 10–6 Torr) to ⟨100⟩ at higher pressures (5 × 10–2 Torr). This observation was attributed to the nature of surface termination and templating effect of the c-YSZ{100} platform at different pressures. With the use of θ–2θ and φ scans of X-ray diffraction, the epitaxial alignment across the NiO/c-YSZ interface was determined to be {111}NiO|||{100}c‑YSZ and ⟨110⟩NiO||⟨100⟩c‑YSZ for the heterostructure grown under a low pressure and {100}NiO||{100}c‑YSZ and ⟨100⟩NiO||⟨100⟩c‑YSZ for the heterostructure grown under a high oxygen pressure. Our high-resolution TEM studies revealed formation of atomically sharp interfaces with no evidence of interfacial reaction and confirmed the established epitaxial relationships. n-Type electrical conductivity was observed in the NiO epilayers grown under lower pressures, which was turned into p-type in the films deposited under higher oxygen partial pressures. Besides, the electrical resistivity increased with the growth pressure. These observations were correlated to the nature of point defects in the NiO crystal. The formation of oxygen vacancies and metallic nickel at lower pressures and excess oxygen and trivalent nickel at higher pressures was revealed by XPS. We established a structure–property correlation in NiO/c-YSZ{100}/Si{100} thin film epitaxial heterostructures with special emphasis on the stoichiometry and crystallographic characteristics.

Polaronic interacceptor hopping transport in intrinsically doped nickel oxide

“…Furthermore, for this sample, the states are widely distributed such that the VRH model applies at all temperatures below 300 K. In contrast to this, for the HT-NiO film, the narrow distribution of states allows charge transfer only between nearest neighbor defects. Based on this model, an explanation can be given why there are some reports on NiO in the literature which claim hole mobilities of more than 1 cm 2 V −1 s −1 , far outside the range typical for polaronic hopping transport [54][55][56][57] . In many of these works, the conductivity of the investigated films is in the range of 1 × 10 −2 S cm −1 and higher, suggesting higher doping levels and thereby a stronger spatial overlap of the ZR wave functions than reported in this work.…”

Investigation on tailoring physical properties of Nickel Oxide thin films grown by dc magnetron sputtering

“…R Moalei et all have reported that the NiO thin films grown at lower oxygen partial pressures behave as n-type and p-type conductivity was observed for the films grown at higher oxygen partial pressures [21]. On the other hand, other research groups have reported both p and n-type conductivity under 9% of oxygen partial pressure and they suggested a p-type conductivity above 9% of oxygen pressure [22].…”

Built‐In‐Homojunction‐Dominated Intrinsically Rectifying‐Resistive Switching in NiO Nanodots for Selection‐Device‐Free Memory Application

“…We would like to point out that, despite the well-known defect chemistry of NiO from earlier studies [45][46][47] suggesting that the main defect species in NiO are Ni vacancies, which are responsible for the p-type conductivity of NiO, the oxygen vacancies are also expected to play an important role at low work-temperatures and low oxygen-pressures. [48] The NiO nanodots in this work were prepared at 500 ℃ and 1.5 Pa oxygen-pressure, which are almost the same with the conditions for NiO films in our previous work, [28] in which the oxygen vacancies in NiO have been observed directly by scanning transmission electron microscopy (STEM).…”