Steplike phonon structures are observed in the luminescence spectrum of porous Si under excitation within the luminescence band at liquid He temperature. The shape of the phonon structures are successfully interpreted in terms of a model based on phonon assisted indirect transitions. From the spacing of the structures, it is concluded that the luminescence occurs in an entity which has a phonon spectrum very similar to crystalline Si. The broad spectrum of luminescence is attributed to an inhomogeneous distribution of the indirect band gap energy of Si particles.

• Received 23 November 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.3659