Resonant interactions of optical phonons with acceptor continuum states in silicon

We have performed and analyzed optical-absorption experiments which provide clear evidence of Breit-Wigner-Fano resonant interactions between the electronic continuum states of acceptors and localized excitations involving optical phonons in silicon. For boron, the 519-cm^-1 zone-center phonon lies within the region of excitation to the continuum of the p3/2 valence band, leading to an antiresonance at that wave number. In addition, antiresonances are observed in silicon doped with boron at 764 cm^-1, aluminum at 962 cm^-1, and gallium at 989 cm^-1. These numbers correspond to the one-phonon sidebands of the bound-to-bound 1S3/2→2P3/2 impurity excitations, which lie within the region of excitation to the continuum of the p1/2 valence band. Fano's theory is used to analyze these results.