MUON-DECAY POSITRON CHANNELING IN SEMICONDUCTORS

The lattice positions of implanted positive muons (mu+) in intrinsic semiconductors (Si, GaAs, InP) have been investigated by mu-decay positron channeling at temperatures ranging from 95 K to 400 K. The positrons exhibit planar steering effects with a maximum amplitude of approximately 5% and a width of the order of 0.1-degrees. In high purity float-zone (FZ) Si a metastable mu-site is observed: Below 200 K, the pattern is consistent with a fraction of 40% near a BC (bond-center) site and 60% near a T (tetrahedral) site. Above 200 K. the T-like fraction undergoes a transition to the BC-like site, where virtually all muons are located above 300 K. By comparison with muon-spin-rotation (mu-SR) measurements, these sites can be associated with the known paramagnetic muonium (mu+-e-) states observed in numerous semiconductors: the metastable site corresponds to the isotropic state (Mu), the BC-like configuration is the stable site for both the anisotropic state (Mu*) at low temperatures as well as the final ionized state ("mu+") at higher temperatures. In GaAs, there is evidence for a similar metastability. In InP, a near-BC configuration is observed throughout the temperature range investigated. There is no indication of a metastable site. Thus a BC-like configuration is found to be most stable in all measurements.