Bond Charge, Bond Polarizability, and Phonon Spectra in Semiconductors

A nonlinear extension of the bond-charge model is used for the analysis of the infrared and Raman spectra because of phonons in diamond, silicon, and germanium. The infrared absorption of these crystals is explained by the anharmonic coupling between the bond charges and their neighboring ions. The first- and second-order Raman spectra are described successfully by means of bond polarizabilities. The relation of the model parameters to the photoelastic constants and band structures is discussed.