The theory of luminescent states in semiconductors: Vibronic interaction

We review the role of vibronic (electron-phonon) coupling in determining the properties and spectra of luminescent states in covalent semiconductors and analyze the consequences of the symmetry of the electronic and vibrational wave functions involved. We show that a degenerate hole or electron state which is strongly coupled to the lattice can produce a Jahn-Teller distortion which markedly modifies its properties. We present calculations of reduction factors for the deformation potentials and g-factors of these states as a function of the strength of their coupling to lattice modes of symmetry E and T2 and discuss the effect of this coupling on the energies and oscillator strengths of bound excitons. As an example we show that the Bi exciton in GaP is strongly coupled to these assymetric modes and that many of its properties are modified as a result. In particular, the large oscillator strength of its B-line emission is due to this coupling, and its binding energy relative to a free exciton is derived almost entirely from the vibronic coupling (including the symmetric A1 modes). The consequences of these results for other states in semiconductors are briefly discussed. © 1970.