Electronic structure of hydrogen donors in semiconductors and insulators probed by muon spin rotation

Shimomura, Koichiro*; Ito, Takashi   

Hydrogen in semiconductors and insulators plays a crucial role in their electric conductivity. Substantial experimental and theoretical efforts have been made to establish this hypothesis in the last decade, and the muon spin rotation technique has played a pioneering role. Positive muons implanted into such low-carrier systems often form a muonium (a hydrogen analogue). Although its dynamical aspect may be different from the heavier hydrogen, the electronic structure of the muonium is expected to be identical to that of hydrogen after a small correction of the reduced mass. Since the discovery of a shallow muonium in CdS, its properties have been intensively studied in many semiconductors and insulators, and then it was interpreted as a possible origin of -type conductivity under the context of a classical shallow donor model. In this article, we will describe the principle of muonium experiments and survey recent achievements in this field.