Transition dynamics for muonium acceptor states in silicon germanium alloys
Jayarathna, Ganga S.
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In this study, we use longitudinal field muon spin relaxation (LF-µSR) technique to observe charge-state and site-change transitions of muonium in Si1-xGex samples (x = 0.45, 0.77, 0.81, 0.84, and 0.94). We primarily focus on modeling the temperature and field dependence of the relaxation data found for muonium to investigate the donor and acceptor ionization energies, paramagnetic hyperfine frequencies and charge-state/ site-change cycles. We attempt to compare the donor/acceptor ionization energies extracted from relaxation data to those obtained by temperature dependency asymmetry fits and verify process assignments of specific dynamics to each observed relaxation feature. We seek to access few energy values that have not been determined previously. Especially we try to find acceptor ionization energies for mid range samples in order to complete the band diagram model. The muonium acceptor level lies within the band gap for Si1-xGex samples between x = 0.45 and 0.84. For x < 0.7, the energy required for the T-site Mu0 to change sites to the bond-centered (BC) donor location is smaller than the MuT ionization energy such that a direct measure of the T-site acceptor level energy is not possible. Previous studies have shown that the T-site muonium acceptor level enters the valence band near x=0.92. Data obtained from this study imply two other muonium acceptor states with muonium trapped at a Si in the anticipated AB_Si locations within the tetrahedral Si_n Ge_(4-n) cage region. Since the hole related dynamics are expected to be active in high Ge content samples we propose a new charge cycle that involves valence band resonant states.