Noble gas as a functional dopant in ZnO

Abstract

Owing to fully occupied orbitals, noble gases are considered to be chemically inert and to have limited effect on materials properties under standard conditions. However, using first-principles calculations, we demonstrate herein that the insertion of noble gas (i.e., He, Ne, or Ar) in ZnO results in local destabilization of electron density of the material driven by minimization of an unfavorable overlap of atomic orbitals of the noble gas and its surrounding atoms. Specifically, the noble gas defect (interstitial or substitutional) in ZnO pushes the electron density of its surrounding atoms away from the defect. Simultaneously, the host material confines the electron density of the noble gas. As a consequence, the interaction of He, Ne, or Ar with O vacancies of ZnO in different charge states q (ZnO:VO q ) affects the vacancy stability and their electronic structures. Remarkably, we find that the noble gas is a functional dopant that can delocalize the deep in-gap VO q states and lift electrons associated with the vacancy to the conduction band.

Giant Piezoelectricity of Deformed Aluminum Nitride Stabilized through Noble Gas Interstitials for Energy Efficient Resonators

“…This indicates that the fraction of Ne atoms at the tetrahedral position will be less compared to Ar and Xe. A similar effect was observed in studies on ZnO, [ 34 ] and it is consistent with our experimental measurement (see Section 2.2.). The calculated formation energies are very similar between relaxation with a fixed and a relaxed lattice (comparing the two panels in Figure 7a).…”

“…These results are also in agreement with theoretical calculations on the analogue wurtzite ZnO. [ 34 ] Experimental evidence also demonstrates that light elements occupy a larger proportion of octahedral interstitial sites. [ 22,35,36 ] Those studies show that for positively charged ions, the substitutional site is thermodynamically favorable, since thermal annealing leads to an increase of substitutional defects.…”

Ti- and Fe-related charge transition levels in β−Ga2O3

“…In this thesis, proton irradiation and H as well as He implantation were utilized [299][300][301]. He is often used for implantation because it will not act as an electrically-active center inside a material [302]. Here, irradiation is distinguished from implantation by the penetration depth for the species the irradiation or implantation is performed with relative to the region of interest.…”

Noble Gas Functional Defect with Unusual Relaxation Pattern in Solids

“…While the primary focus of this research does not lie on an exact comparison of defect formation energy as a function of the distance between the noble gas and the vacancy, it is important to note that, in many scenarios, noble gas defects opt for the vacancy site, which presents itself as the lowest energy configuration. 25 When noble gas defects are located away from the vacancy site, their impact on electronic properties is relatively insignificant, unless they disrupt the chemical bonds between the host atoms. Conversely, when a noble gas occupies the vacancy site, there is a shift of electrons from the occupied in-gap state to the principal conduction band�essentially, two electrons are transitioned to the conduction band while the localized in-gap states vanish.…”

“…This technique specifically relies on the assumption that Ar defects do not modify the material properties. Although noble gases (at least He, Ne, and Ar) are considered chemically inert due to their fully occupied orbitals, they can still influence material properties through repulsion with atomic orbitals of surrounding atoms and even under certain conditions form compounds (at least heavy noble gas elements having smaller ionization energy). − This repulsion can result in changes to the charge density distribution, effectively making the noble gas a functional defect . However, a fundamental question remains: Does the noble gas have a substantially different effect on other material properties beyond functionality?…”