Interactions of $_\mu$Al acceptor impurity in weakly and heavily doped silicon

The interactions of the aluminum acceptor impurity in silicon are investigated using polarized negative muons. The polarization of negative muons is studied as a function of temperature on crystalline silicon samples with phosphorus ($1.6\times10^{13}\,$cm$^{-3}$) and boron ($4.1\times10^{18}\,$cm$^{-3}$) impurities. The measurements are performed in a magnetic field of 4.1 kG perpendicular to the muon spin, in the temperature range from 4 to 300 K. The experimental results show that, in phosphorus-doped $n$-type silicon, an $_\mu$Al acceptor center is ionized in the temperature range $T>50\,$K. For boron-doped silicon, the temperature dependence of the shift of the muon spin precession frequency is found to deviate from the $1/T$ Curie law in the temperature range $T\lesssim50\,$K. The interactions of a $_\mu$Al acceptor that may be responsible for the effects observed in the experiment are analyzed.