The electrical activity of hydrogen and muonium in silicon at high temperatures

Above 500 K in silicon, isolated hydrogen defect centres scatter intrinsic charge carriers strongly by momentary formation of the neutral atomic ground state, located at the tetrahedral cage centre. This is inferred from the analogous behaviour of muonium, via distinctive muon spin rotation and relaxation signals. A consistent interpretation of a surprisingly large shift of the muon Larmor frequency and the strong transverse and longitudinal spin relaxation rates is achieved in terms of charge-state transition rates into and out of the neutral paramagnetic state. The nature of the charge cycle and the interplay with the crystallographic site are discussed and the electrically active level in the energy gap is determined. (C) 2003 Elsevier B.V. All rights reserved

Location of the hydrogen donor in InN: Evidence from muonium results

Muon spin depolarization measurements in a zero applied magnetic field confirm the existence of a shallow muonium (Mu) donor in InN, consistent with earlier transverse-field muon spin precession results. The zero-field data imply two Mu(+) centres in InN, similar to those associated with channel and cage sites in GaN. The zero-field results provide strong evidence that the shallow Mu(0) ionizes to Mu(+) at its lowest-energy location. We argue that data on Mu in the III-V nitrides, taken in total, support the assignment of a wurtzite channel location to the shallow hydrogen donor in InN. The present results yield 15.4 +/- 2 meV below the conduction band edge for the donor level depth

Trapping of mobile Mu centers in single crystal AlN

We have investigated muonium (Mu) defect centers in single crystal AlN as an analog for atomic hydrogen impurities. A nitrogen-related muon level-crossing resonance is associated with a static center formed by trapping of a mobile Mu impurity at another defect. This trapped Mu is released above 800 K. Muon spin depolarization data imply that both Mu(0) and ground-state Mu(+) centers are mobile. Strong correlations between growth of the trapped Mu resonance and Mu(0) motion and transformation rates above 400 K imply that Mu(0) is the more likely precursor in that region. (C) 2003 Elsevier B.V. All rights reserved

Diffusion and trapping of Mu in the III-V nitrides

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

Muonium-acceptor interactions in gallium phosphide

Zero-field muon spin depolarization measurements on heavily Zn-doped p-type GaP reveal several different states related to the Mu(+) defect center. We find that the Mu(BC)(+) ground state becomes mobile near 200 K. At slightly higher temperature Mu+ motion involves a second site, suggested to be T(P), which is relatively long lived up to 270 K. Zn-Mu complexes are formed at both low and high temperatures by reaction of Zn with a mobile Mu center, Mu(T)(0) below 100 K and Mu(T)(+) above 400 K. The high-temperature complex dissociates above 700 K with a characteristic energy of 1.3 eV. (C) 2002 Elsevier Science B.V. All rights reserved

Characterization of a GaAs/GaAsBi pin solar cell

The structural and photovoltaic properties of the GaAs/GaAsBi pin solar cell with GaAs0.983Bi0.017 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

Motional characteristics of positively charged muonium defects in In 2 O 3

We report on a study of the motional characteristics of positively charged muonium defect centers in In2O3 powder. Zero field muon spin relaxation (ZF-MuSR) measurements were taken from 2 K to 950 K. Results show the positively charged muonium defects occupying two states (Mu(1) and Mu(2)) at low temperatures while a third state (Mu(3)) is introduced as the temperature is increased. Mu(1) is occupied more heavily than Mu(2) at low temperatures by a ratio of +/- 8: 1. The Mu(1) state changes to the Mu(2) state starting at 300 K with site change energy of 0.46+/-0.11 eV and is essentially not occupied above 500 K. The Mu(2) state becomes diffusively mobile with a barrier of 0.78+/-0.07 eV at 350 K and begins trapping at Mu3 at 400 K with a capture energy of 0.56+/-0.019 eV. A metastable region is observed between 500 K and 650 K in which the ratio between Mu(2) and Mu(3) amplitudes and the hop rate of Mu(2) are both roughly constant, implying a steady state trap and release balance between mobile Mu(2) centers and the Mu3 trap state. Above 650 K, the muonium defects release from the Mu(3) trap to the Mu(2) diffusive state with a dissociation energy of 0.901+/-0.003 eV. The upper limit on the high temperature diffusion barrier is determined, from the Mu(2) hop rate, to be 0.43+/-0.03 eV

Motion of positively charged muonium in ZnO

We report on a study of the motional characteristics of positively charged muonium defect centers in ZnO as an analog for H+ behavior. Muon spin depolarization measurements at zero applied magnetic field were completed from 20 K to 400 K, with preliminary results to 750 K. Results at the lower temperatures imply that Mu(+) occupied two sites, and indicate local motion as thermally assisted tunneling with a characteristic energy of similar to 60 meV, as well as a site change transition above 200 K with barrier energy similar to 440 meV. Based on theoretical results, we have tentatively assigned these features to tunneling among three equivalent oxygen anti-bonding sites (AB(perpendicular to)) and a transition to a lower-energy bond-centered site (BC parallel to) oriented along the c-axis. Preliminary fits suggest that global diffusion of muonium occurs above 400 K, with a diffusion barrier energy of similar to 0.7 eV. Published by Elsevier B.V

Muonium in 4H silicon carbide

Data for low-field muon spin rotation spectra for 4H-SiC is presented for a wide temperature range from 10 to 1400 K. At low temperatures, dependence of amplitude transitions for all the samples show carrier capture processes. For p-type sample in the intermediate temperature region transition energies imply both donor and acceptor ionizations. In n-type and high resistivity samples a fast decaying component is observed for temperatures between 900 and 1400 K. Amplitude of this signal as the temperature is elevated starts to dominate, implying that the center represented by this signal is the ground charge state for both samples. We will discuss some of the amplitude transitions and give the energy values associated with these transitions. (C) 2009 Elsevier B.V. All rights reserved

Muonium defect states and ionization energies in SiGe alloys

The determination of hydrogen energy levels in semiconducting materials is important owing to the ability of hydrogen impurity to either compensate dopant activity in some materials or to act as a dopant itself in others. Although direct observation of hydrogen levels is difficult owing to its high mobility and reactivity, data can be provided using the hydrogen analog muonium, formed by implantation of positive unions. We present here muonium studies of bulk Si(1-x)Ge(x) alloys aimed at extraction of hydrogen energy levels within this system. A simple band alignment model predicts the behavior of donor and acceptor muonium species across the alloy range. This model is compared with experimentally determined donor and acceptor levels extracted from the temperature dependence of muonium amplitudes. (c) 2007 Elsevier B.V. All rights reserved