The first 25 years of semiconductor muonics at ISIS, modelling the electrical activity of hydrogen in inorganic semiconductors and high-κdielectrics

Abstract

Early muonium studies provided the very first atomistic pictures of interstitial hydrogen in semiconductors. By the time ISIS muons came on line, the main crystallographic sites, and the electronic structures for the neutral centres, were established in archetypal materials such as Si and GaAs. The results were quite unanticipated, and raised awareness of this deceptively simple defect system. This paper marks contributions to the subject made using ISIS muon beams, in the first 25 years of their operation since 1987. By this time, hydrogen was understood to be a significant and unavoidable impurity in all electronic grade material, and attention was turning to the interaction with charge carriers, revealing an equally unanticipated interplay of site and charge state. In particular, muonium spectroscopy now provides a model for hydrogen in dozens of materials where hydrogen itself is difficult or impossible to study directly, and is able to predict its effect on the electronic properties of new materials, such as those envisaged for optoeletronic or dielectric applications. Donor, acceptor and so-called pinning levels are known in a good many of these materials, revealing intriguing systematics and providing severe tests and challenges to current theory. Progress and prospects are summarized in this report, addressing the obvious questions such as ‘why, how and what next?’

Barrier model in muon implantation and application to Lu2O3

“…Muon spin rotation (μSR) is a widely used method in materials science [1,2]. The muons are implanted into the material, come to rest at an interstitial site, and finally form characteristic states which are distinguishable in the μSR experiment.…”

“…These materials find increasing interest and application in modern electronic devices [24][25][26]. The goal of the muon spin spectroscopy experiments is to obtain a microscopic understanding of these materials on an atomistic scale, in particular regarding the characterization of the hydrogen impurity, which is adequately modeled by the muonium analog [2,4,5]. This work has been performed often in conjunction with ab initio DFT calculations on the same systems [27][28][29][30][31].…”

Role of the transition state in muon implantation

“…In condensed mater positive muons behave similarly to hydrogen and are often used in materials research as local probes and substitutes for hydrogen [1,2]. In muon spectroscopy experiments muons are implanted in the material and come to rest at a site which may not be the final position.…”

Isolated hydrogen configurations in zirconia as seen by muon spin spectroscopy andab initiocalculations

“…From the experimental point of view, the use of muonium (the hydrogenic atom possessing a positive muon as the nucleus: μ + e − ) as a light pseudoisotope of hydrogen has become standard in order to obtain information regarding the electronic states of isolated hydrogen in materials [15][16][17][18]. Although the muon is only one-ninth the mass of the proton, the reduced mass of muonium is 99.6% that of hydrogen, so that the respective electronic properties are basically the same in both atoms.…”