T. L. Estle

PRELIMINARY CALCULATIONS CONFIRMING THAT ANOMALOUS MUONIUM IN DIAMOND AND SILICON IS BOND-CENTERED INTERSTITIAL MUONIUM

The model of anomalous muonium as bond-centered interstitial muonium has been examined by approximate ab-initio Hartree-Fock calculations in diamond and silicon and found to be in excellent agreement with experiment.

Muonium centers in the alkali halides

Muonium centers (Mu) in single crystals and powdered alkali halides have been studied using the high-timing-resolution transverse field μSR technique. Mu has been observed and its hyperfine parameter (HF) determined inevery alkali halide. For the rocksalt alkali halides, the HF parameter Aμ shows a systematic dependence on the host lattice constant. A comparison of the Mu HF parameter with hydrogen ESR data suggests that the Mu center is the muonic analogue of the interstitial hydrogenHi0-center. The rate of Mu diffusion can be deduced from the motional narrowing of the nuclear hyperfine interaction. KBr shows two different Mu states, a low-temperatureMuI-state and a high-temperatureMuII-state.

A review of the experimental results on impurity centers in elemental semiconductors obtained by μSR and other techniques

Selected electron paramagnetic resonance studies of defect centers in group IV semiconductors are reviewed. Features of this research which are useful in analyzing the nature of normal and anomalous muonium (Mu and Mu*) in these crystals are pointed out, and a moderately specific model of Mu and Mu* is presented and compared to studies of hydrogen in silicon and germanium.

MUONIUM IN SEMICONDUCTORS AND SOME IMPLICATIONS FOR HYDROGEN IMPURITIES

A description of the structures, charge states, and the transitions among them for isolated interstitial muonium in covalent semiconductors is presented. This description appears to be general, explaining a wealth of experimental observations on group IV and III–V semiconductors. Observations which support various features of this general description will be presented. A brief mention of some implications for hydrogen in semiconductors will follow.

Longitudinal relaxation of muonium in Ge and GaAs

Longitudinal-field muon-spin depolarization rates in high-purityGe and semiinsulatingGaAs are reported and compared to similar data for intrinsicSi. Depolarization onset temperatures provide a comparison of charge carrier concentrations leading to rapid charge exchange and a shift in the onset, for n-typeGaAs verifies anelectron process. The temperature dependence of the low-field rate constants imply more complicated dynamics inGe than observed earlier inSi. Features near 750K inGaAs∶Te appear consistent with dissociation of aMu-Te pair.

Muonium states in zincblende-structured compounds

The authors present a list of results of μSR experiments in materials with the diamond and zincblende structure. Besides the muonium hyperfine parameters, additional information is tabulated: the formation probability for the different muon states, the highest temperatures at which muonium states have been observed and the types of transitions found to occur between these states. The muonium hyperfine parameters show a linear rise as a function of host ionicity from Ge to GaAs to ZnSe followed by a sharp drop to CuBr.

Muonium states in silicon carbide

Implanted muons in samples of silicon carbide have been observed to form paramagnetic muonium centers (μ+ e−). Muonium precession signals in low applied magnetic fields have been observed at 22 K in a granular sample of cubic β-SiC, however it was not possible to determine the hyperfine frequency. In a single crystal sample of hexagonal 6H-SiC, three apparently isotropic muonium states were observed at 20 K and two at 300 K, all with hyperfine frequencies intermediate between those of the isotropic muonium centers in diamond and silicon. No evidence was seen of an anisotropic muonium state analogous to the Mu* state in diamond and silicon.

Some simple thoughts about the structure of anomalous muonium

The subject of this paper is anomalous muonium and the kind of model that can be given to explain its observed properties. The implications of experimental findings on a model are discussed and several possible models are suggested. No clearly superior model yet exists, in part because of a lack of theoretical studies of possible models and in part because of the lack of sufficiently definitive experiments.

DIAMAGNETIC MUONIUM STATES IN INP

Transverse and zero‐field muon spin relaxation reveal several diamagnetic muonium states in InP characterized by their static linewidths and diffusion properties. We tentatively associate low‐temperature diamagnetic states with Mu+ in the BC and TP interstitial sites and a missing fraction with Mu0 rapidly diffusing through TIn interstices. Trapping peaks above 250 K imply static centers which depend on doping type, consistent with Mu- at TIn for n‐type samples and Mu coupled with a dopant or other defect for p‐type.

Final states in Si and GaAs via RF μSR spectroscopy

The ionization of muonium centers in Si and GaAs have been studied using radio frequency (RF) resonant techniques. In Si all three muonic centers are detectable by RF. No evidence was found for delayed Mu and Mu* states at any temperature. However, our results on the diamagnetic final state (μf+) show that it is composed of prompt fractions (as seen by conventional μSR) and delayed fractions arising from the ionization of Mu* and Mu. We observe a full μf+ fraction at 317 K when the Mu relaxation rate is above 10 μs−1. GaAs differs from the situation in Si in that we observed only a partial conversion of Mu* and Mu to a μ+ final state up to 310 K in spite of the fact that the transverse field relaxation rates become very high at 150 and 250 K respectively.