Spectroscopic studies of double donors in silicon

Abstract

In this paper we briefly review optical excitation spectroscopy of isolated double donors silicon. We discuss how energies of optically forbidden states may be determined, either i) from phonon-assisted Fano resonances above the ionization limit; or ii) by shifting forbidden states into resonance with allowed transitions through the application of uniaxial stress. For neutral donors with two bound electrons, the importance of many-body effects has recently been demonstrated by a first study of spin-triplet states under uniaxial stress. We discuss the implications for the electronic structure of double donors' and the question whether these systems may be viewed as solid-state analouges of helium. Finally, for singly ionized double donors, we find that the behavior of the deepest excited states under uniaxial stress cannot be accounted for within effective-mass theory and the deformation-potential approximation.