Identification of Li$_{\text{Ni}}$ and V$_{\text{Ni}}$ acceptor levels in doped nickel oxide

TL;DR

This study experimentally determines the energetic positions of Li_Ni and V_Ni acceptor levels in doped nickel oxide using defect spectroscopy techniques on heterojunctions, providing key insights into their electronic structure.

Contribution

The paper experimentally identifies the charge transition levels of Li_Ni and V_Ni acceptors in NiO, which were previously unknown.

Findings

Li_Ni acceptor level at 190 meV above valence band

V_Ni acceptor level at 409 meV above valence band

Use of capacitance-voltage and thermal admittance spectroscopy for defect characterization

Abstract

Nickel oxide, in particular in its doped, semiconducting form, is an important component of several optoelectronic devices. Doping NiO is commonly achieved either by incorporation of lithium, which readily occupies Ni sites substitutionally, producing the Li$_{\text{Ni}}$ acceptor, or by supplying reactive oxygen species during NiO film deposition, which leads to the formation of Ni vacancies (V$_{\mathrm{Ni}}$). However, the energetic position of these acceptors in the NiO band gap has not been experimentally determined until today. In this work, we close this knowledge gap by studying rectifying n$^{++}$p heterojunctions of NiO on top of fluorine-doped tin oxide. These structures show sufficient rectification to perform electric characterization by defect spectroscopic techniques, specifically capacitance-voltage and thermal admittance spectroscopy. Using these methods, the (0/-) charge transition levels are determined to be 190meV and 409meV above the valence band edge for the Li$_{\text{Ni}}$ and the V$_{\text{Ni}}$ acceptor, respectively.