  We have measured the optically injected excess carrier lifetime in silicon
using photoexcited muon spin spectroscopy. Positive muons implanted deep in a
wafer can interact with the excess carriers and directly probe the bulk carrier
lifetime whilst minimizing the effect from surface recombination. The method is
based on the relaxation rate of muon spin asymmetry, which depends on the
excess carrier concentration. The underlying microscopic mechanism has been
understood by simulating the four-state muonium model in Si under illumination.
We apply the technique to different injection levels and temperatures, and
demonstrate its ability for injection- and temperature-dependent lifetime
spectroscopy.
