Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In 2 O 3 and SnO 2 . The paramagnetic charge state is stable below ϳ50 K in In 2 O 3 and ϳ30 K in SnO 2 which, coupled with its extremely small effective hyperfine splitting in both cases, allows its identification as the shallow-donor state. This has important implications for the controversial issue of the origins of conductivity in transparent conducting oxides.
By using photoexcitation, we unambiguously establish that the well-known diamagnetic muonium spin precession signal in Ge is in fact due to two diamagnetic states. Their temperature dependences are studied up to room temperature. The signal due to one of these states is strongly influenced by the photoexcited carriers while the other is not. The identification of these two centers is discussed.
The structural and photovoltaic properties of the GaAs/GaAsBi pin solar cell with GaAs 0.983 Bi 0.017 active layer are investigated by optical and electrical measurement techniques. The bandgap of GaAsBi active layer is determined to be 1.3 eV at room temperature. Current density-voltage (J-V) under AM 1.5G spectrum and spectral response measurements are carried out to determine photovoltaic properties of the solar cell. The presence of a midgap trap levels in GaAsBi active layer is identified by deep level transient spectroscopy (DLTS). J-V characteristics is analysed by using Sah-Noyce-Shockley (SNS) theory which includes the midgap trap found in DLTS measurement. The observed deviation between experimental and calculated J-V results is ascribed for metallic cluster formation at the interface between GaAs emitter and GaAsBi intrinsic active layer. Interface metallic clusters create local Schottky junction between emitter and active layers. The best fit to the experimental J-V characteristic of the solar cell is obtained by considering the presence of GaBi metallic cluster at the interface between GaAs emitter and GaAsBi active layer of the solar cell. We showed that work function of interface clusters have a significant effect on the open circuit voltage and filling factor.
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?’
Sites and dynamics obtained for muonium (Mu) defect centres provide a good experimental model for the behaviour of the equivalent hydrogen impurities. We discuss the dynamic properties of Mu centres in the III-V nitrides focusing on features common to the three materials. Muon spin depolarization data in zero magnetic field provide motional dynamics for the Mu + and Mu − charge states and field dependent longitudinal relaxation rates probe motion of Mu 0 centres. The data also show dynamics associated with metastable locations, either intrinsic to the wurtzite structure or defect related, including trapping and release transitions. A general picture of the behaviour of H in the III-V nitrides is developed from these measurements for comparison to theoretical results.
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