Isotope effects in the electronic spectra of singly ionised S and Se donors in silicon

We report on the observation of weak satellites of the strong and sharp parity-forbidden, but symmetry-allowed 1s(A1)-1s(T2) doublet of the infrared electronic spectrum of S + in silicon. The low-energy satellites are ascribed to a Si isotope effect and the high-energy ones to an S isotope effect. We also show that the profile of the low-energy component of the same transition of Se can be reproduced from the computed combination of Si and Se isotope effects with the same global characteristics as those of S. These shifts are discussed in terms of the effect of the Si-chalcogen bond softening in the electronic ground state and of a Jahn–Teller coupling of the electronic excited state with a triply degenerate vibrational mode of a cluster involving the chalcogen atom and its first nearest neighbours. r 2003 Elsevier B.V. All rights reserved. PACS: 63.30.Mt; 71.55.Cn; 78.30.Am