We report the observation of a resonance in the infrared-absorption spectrum of heavily boron-, aluminium-, and gallium-doped silicon at room temperature. This resonance occurs near the frequency of the zone-center optical phonon (517 ${\mathrm{cm}}^{\mathrm{-}1}$) and is attributed to a discrete-continuum Fano-type resonant interaction between the optical phonon and direct inter-valence-band transitions of holes. The optical-phonon transitions are allowed due to the disruption of symmetry of the crystal lattice by acceptor atoms. The dependence of the resonance on doping level is investigated.

• Received 18 April 1995

DOI:https://doi.org/10.1103/PhysRevB.52.5672