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Long‐Wavelength Optical Phonons in Mixed Crystals . II. The persistence of common gaps
Author(s) -
Jahne E.
Publication year - 1976
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220750123
Subject(s) - phonon , condensed matter physics , wavelength , lattice (music) , mode (computer interface) , eigenvalues and eigenvectors , physics , impurity , band gap , formalism (music) , materials science , optics , quantum mechanics , computer science , art , musical , acoustics , visual arts , operating system
The formalism developed in Part I in order to describe the long‐wavelength optical phonons in mixed crystals as a system of two coupled modes is now applied to the two mixed systems In 1 – x Ga x P and GaAs 1 – x P x as representative ones for one‐ and two‐mode behaviour, respectively. Calculated mode frequencies, eigenvectors, and infrared oscillator strengths are presented and their behaviour is discussed in dependence on composition in both mixed systems. Contrary to earlier suggestions we state that in a traditionally named one‐mode system apart from the lattice‐like mode in addition an impurity‐like mode occurs which is always an in‐band mode. A two‐mode system is characterized by a gap between the two sets of optical phonons arising from a gap between the optical phonon bands of the end‐member crystals. A new criterion is given for one‐ or two‐mode behaviour in terms of an overlapping or the existence of a gap between the optical phonon densities of states of the end‐member crystals. It is suggested from several items that the persistence of common gaps of the end‐member crystals is a determining factor in the lattice dynamics of mixed systems.