The Effect of Optical Mode Phonons on the Absorption Spectra of Shallow Impurity Centres

The interaction between optical lattice vibrations and carriers bound in shallow impurity levels in diamond structure crystals is investigated. It is shown that, while electronic transitions assisted by the emission of optical mode phonons are likely to produce easily observable infra-red absorption peaks in diamond, the corresponding peaks are not likely to be observable in the absorption spectra of doped silicon and germanium. An attempt is made to show that these optical phonon-assisted transitions will also be difficult to observe for deep-lying levels in silicon and germanium.