Shallow Impurity Absorption Spectroscopy in Isotopically Enriched Silicon

Impurity absorption spectroscopy of the deep double donor sulfur in isotopically enriched silicon

“…The natSi and 30Si samples also exhibit a tail on the low energy side for the first and on the high energy side for the latter. This is similar to the tails observed for phosphorus transitions in natural silicon [9]. Photon energy (ern") Figure 4.14: 8°2p± in four different samples.…”

“…Labels were assigned with the help of data given in [12] for SO and in [10] for sg (this data had to be scaled to low energy So transitions). In contrast to this we observe an increasing shift in energy in between the different silicon isotopes for higher excited states, similar to Band P absorption transitions [8,9]. As outlined in Section 2.3.1, the dependence of EO and m* on the isotopic mass scales the ground state and excited state binding energies by an identical factor, and thus the largest shifts are observed for transitions to the highest excited states.…”

“…Essentially the p-state spectra have features identical to the ones observed for shallow group V donors in silicon, such as the prototypical phosphorus impurity [9].…”

“…Another consequence is that an impurity centre can have a varying binding energy whenever the average host isotope mass in its vicinity is different from the average isotopic composition of the host material. For phosphorus and boron impurity centres this is believed to cause both broadenings and tails on the absorption lines [9].…”

“…In this spectrum we measure a FWHM of only 0.008cm-1 for the 1s(T 2 ) r 7 line and 0.022cm-1 for the r 8 absorption line. The r 7 transition is, together with Se in 28Si [35] the narrowest donor or acceptor absorption line observed in silicon to date -it is 22 times narrower than in previous S spectra [11] and narrower than P and B absorption transition lines in 28Si by a factor of two [9]. This exceptional result can be explained by the fact that the 1s(A 1 )~1s(T 2 ) transition is EMT forbidden but symmetry allowed and thus has a long radiative lifetime.…”