Ionization mechanisms of aluminum acceptor impurity in silicon

Processes of ionization of shallow acceptor centers (ACs) in silicon are studied. In crystalline silicon samples with phosphorus (1.6×10¹³, 2.7×10¹³, and 2.3×10¹⁵cm^‑3) and boron (1.3×10¹⁵cm^‑3) impurities, _μAl impurity atoms were produced by implantation of negative muons. It is found that thermal ionization is the main mechanism for ionizing the Al acceptor impurity in both p-type and n-type silicon with an impurity concentration of ≲10¹⁵cm^‑3 at T>45 K. The thermal ionization rate of Al ACs in Si varies from ∼10⁵ to ∼10⁶s^‑1 in the temperature range 45–55 K.