2-DIMENSIONALLY LOCALIZED TO-PHONON MODE DUE TO MONATOMIC AL LAYERS EMBEDDED IN GAAS

Vibrational properties of a single slab of Al atoms substituting for a (001) Ga monatomic layer in GaAs were investigated by use of infrared-absorption spectroscopy. A specific absorption peak was observed at 358 cm-1. Systematic investigations of the infrared absorption for superlattices having various numbers of AlAs and GaAs layers showed that the peak is a TO-phonon mode due to two-dimensionally distributed Al atoms, being strongly localized at the layer. This result demonstrates the existence of the two-dimensionally localized vibrational mode due to monatomic impurity layers embedded in three-dimensional covalent semiconductor crystals.