Further investigations of the deep double donor magnesium in silicon

The deep double donor levels of substitutional chalcogen impurities in silicon have unique optical properties which may enable a spin/photonic quantum technology. The interstitial magnesium impurity (Mg_i) in silicon is also a deep double donor but has not yet been studied in the same detail as have the chalcogens. In this paper, we look at the neutral and singly ionized Mgi absorption spectra in natural silicon and isotopically enriched 28-silicon in more detail. The 1s(A1) to 1s(T2) transitions, which are very strong for the chalcogens and are central to the proposed spin/photonic quantum technology, could not be detected. We observe the presence of another double donor (Mg_i∗) that may result from Mg_i in a reduced symmetry configuration, most likely due to complexing with another impurity. The neutral species of Mg_i∗ reveal unusual low-lying ground state levels detected through temperature dependence studies. We also observe a shallow donor which we identify as a magnesium-boron pair.