DEFECTS IN CRYSTALS STUDIED BY RAMAN-SCATTERING

Raman studies of crystal defects are reviewed. Raman spectroscopy is a powerful technique and has been used widely for investigating disorde red structures. The degree of disorder in a crystal is quantitatively evaluated in terms of the phonon correlation length. The asymmetric Ra man line shapes in defective crystals such as microcrystals, ion-impla nted semiconductors are well reproduced by the spatial correlation (SC ) model. The effect of alloying induced-potential fluctuations on Rama n scattering is also explained within the framework of the SC model. I n disordered graphite, the in-plane phonon correlation length is obtai ned from the relative intensity ratio of the disorder induced peak. Th e initial lattice disordering rates and the relaxation rates of disord er are determined, using real-time Raman measurements during ion irrad iation in a scale of seconds. In this way, the phonon confinement due to the local defects is observed in the kinetic manner. Localized vibr ational modes of defects in crystals are also described. In particular , Raman observation of the hydrogen molecule in crystalline semiconduc tors is discussed in detail.