An Isoelectronic Acceptor the Be2 Pair in Silicon

Line A was also observed in absorption and PLE measurements near 2 K. In the PLE spectrum of line B, other weaker lines were reported at energies between 1110 and 1114meV, and they were attributed first to the transitions toward the excited states of the IBE. Inversely, in the PL measurements at 1.2 K, only line B was observed (with a weak contribution of line B) while at 15 K, line A predominated, and at 40K, two weak PL lines due to recombination from the excited states were also observed [176]. 

The two weaker lines observed in PL near 1115meV (A and B at 1117.0 and 1115.21 meV, respectively) were initially attributed to the recombination 

The long lifetime (480 ps) measured by [176] for the 12, 2) excited state of B allowed to perform absorption measurements in the far IR similar to those7 on the Sa and Sb IDs. The results of these measurements demonstrated without ambiguity that the (Bes, Be ) pair was indeed an isoelectronic acceptor [106,175]. The difference between the far-IR spectra of a Be-doped silicon sample under above-band-gap illumination and under TEC are displayed in Fig. 7.21 at different temperatures and compared with the p3/2 

7 This far-IR spectrum on the (Bes, Bei) pair actually provided the first results on the odd-parity states of an IBE shallow-impurity-like centre. 

At the lowest temperature, three acceptor lines denoted 1 B, 2 B, and 3B are observed at 27.51, 31.44, and 36.50meV, respectively, and from comparison with the P3/2 (B) spectrum, their excited states are comparable to the 1 Tg-, 2Ts-, 1 TfA 1 IV, respectively, in Td symmetry. Their ground state is the IBE 2, 2) substate, and for higher temperatures, the thermalization of the other sublevels of the IBE ground state gives lines nB, nB , and 11A, with n = 1, 2, and 3. In the shallow acceptors numbering 4 of Table 7.2, lines IB, 2B and 3B correspond to lines 1, 2, and 4-6 of the p3/2 spectrum of group-III acceptors. 

---