Magnesium-related shallow donor centers in silicon

Magnesium (Mg) atoms, diffused in silicon (Si) lattice at high temperatures, tend to form specific bonds to host Si atoms, to other Mg atoms as well as to other defects in a Si crystal. These electrically active donors exist either as isolated atomic type centers or as complexes coupling magnesium to other trace elements in silicon. We report on shallow Mg-related donor centers in moderately doped Si:Mg crystals which are distinguished by their infrared absorption spectra. These complexes have energy spectra, relatively dense filling two separated infrared ranges, 30–95 meV and 105–130 meV, having clearly different genesis. These centers are observed in silicon of various purification degree, including high-purity crystals with low oxygen and carbon content. We assign the formation of such localized states in Si:Mg to electrically active donor complexes with different numbers of magnesium atoms, similar to those formed by interstitial oxygen in silicon. The results obtained are incorporated into the general phenomenon of formation of shallow donors in silicon which is related to interaction of impurities in the semiconductor.