The modelling of hydrogen in amorphous and glassy semiconductors

The behaviour of hydrogen in crystalline and amorphous semiconductors has been simulated using the positive muon as a microscopic probe. Measurements have been made on a wide range of materials: polycrystalline and amorphous silicon, both doped and intrinsic; polycrystalline and amorphous germanium; crystalline CaAs and GaP; and selenium-based glassy chalcogenides. Using the techniques of SR (Muon Spin Resonance/Rotation/Relaxation/Repolarisation), the evolution of the spin polarisation of the muon is monitored. In semiconductors and insulators, the muon is bonded to an electron to form muonium (Mu=+e-) and it is this species that behaves as an analogue of isolated atomic hydrogen. The muon spin polarisation is greatly influenced by the local environment, and its study has yielded information on the sites occupied by the muon/muonium, via determinations of diamagnetic fractions and hyperfine parameters. The technique of muon spin repolarisation has been used for the first time in conjunction with recently derived theoretical expressions to extract this information. Preliminary measurements using the technique of muon spin resonance on a newly developed facility at the Rutherford Appleton Laboratories has also been made.