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 in silicon is also a deep double donor but has not yet been studied in the same detail as have the chalcogens. In this study we look at the neutral and singly ionized Mgi absorption spectra in natural silicon and 28-silicon in more detail, looking in particular for the 1s(A1) to 1s(T2) transitions which are very strong for the chalcogens and are central to the proposed spin/photonic quantum technology. We further observe the presence of another donor (Mgi∗) that may result from Mgi in a reduced symmetry configuration, due to either complexing or the occupation of an interstitial site with symmetry lower than the usual tetrahedral site. The neutral species of Mgi∗ reveal additional low lying ground state levels detected through temperature dependence studies. We also observe a new shallow donor which we identify as an Mg-B pair center. Additionally we present photoluminesence spectra that verify the existence of an Mg-Mg isoelectronic pair center through its isotopic fingerprint. We further include the results of a temperature dependence and photoluminesence lifetime study of this same center, revealing unusual behaviour of the main no-phonon line and associated phonon replicas.