Evidence for a shallow muonium acceptor state in Ge-rich Cz-Si_{1 - x} Ge_x

We have observed muon spin rotation (μ SR) features that are consistent with a shallow muonium (Mu) acceptor state for several Ge-rich silicon germanium alloy compositions. The Mu_T [0 / -] defect level crosses into the valence band at a Ge content of roughly 92%, indicating that a shallow acceptor state should be formed for muons that stop in the acceptor related T-site. For Si_0.09 Ge_0.91, the difference between the diamagnetic amplitudes from RF-driven resonance measurements compared to TF- μ SR indicates a slowly formed state at temperatures below 50 K, consistent with a valence-band resonant Mu^- that would form the core of a shallow Mu acceptor. We report a summary of hyperfine characterization and transition energies of the various T-site muonium states in Ge-rich alloys and discuss options for the conditions under which shallow acceptor states may be observed by μ SR.