Hydrogen impurities in p-type semiconductors, GeS and GeTe

Abstract

Hydrogen defects sometimes form shallow impurity levels in semiconductors, and it is an important topic for semiconductor research to investigate their details. One of the experimental methods to determine the state of hydrogen is the muon spin rotation (μSR) experiment. By observing formation of a pseudo-hydrogen atom, called muonium, it is possible to investigate the hydrogen defect levels. In a previous theoretical study, the pinning levels were calculated for various materials as a reference for hydrogen defect levels, and these levels were universally distributed near the hydrogen electrode potential. Based on the prediction, μSR experiments were performed for germanium sulfide (GeS) and germanium telluride (GeTe), where the hydrogen electrode potential is located in the bandgap for GeS, but not for GeTe. As a result, the μSR spectra showed that the muonium forms in GeS, while it does not in GeTe. In GeS, 58% of the muons formed muoniums. The activation energy was obtained as ΔE=26.2±6.9 meV. The hyperfine coupling frequency was ωc(2π)−1=1.95±0.17 GHz, and the Bohr radius of muonium was 1.3 times larger than that in vacuum. These properties indicated that the identified muonium does not form a typical impurity level that affects the electrical properties.