We present a detailed analysis of the interaction between intrinsic localized modes and plasmons in a doped polar semiconductor. The investigation has been performed for an anharmonic one-dimensional diatomic lattice with alternating interactions coupling successive neighbours. The system simulates a row of atoms in the <111> direction of a III-V semiconductor. Specific calculations have been performed for GaN, because it has a large gap between the acoustic and optical phonon branches. The calculations of the intrinsic localized modes have been performed by using two-body potentials to describe the interactions. We have used the rotating wave approximation and we have found the intrinsic localized modes in the phonon gap. The interaction with the plasmon has been studied by adding to the equations of motion the alternating electric field which is related to the electron density of the plasmons. We obtain an expression for the electric dynamical polarization associated with the intrinsic localized modes and with the plasmons. We derive an expression for the dielectric function of the coupled system. The zeros of the dielectric function give the frequency of the combined modes. We have found two regimes in which combined modes are possible. One is related to small anharmonicity of the potential. The combined mode has a frequency above the top of the optical branch and can be explained in terms of the theory of the harmonic dielectric response of polar lattice vibrations. The second regime is related to high anharmonicity. The combined modes exist only for a finite slab. We show that on increasing the anharmonicity, i.e. the amplitude of the intrinsic localized mode, the width of the slab increases. The frequency of the combined mode is inside the phonon gap. We have also studied the dynamical stability of these modes.
Coupling of intrinsic localized modes in doped polar semiconductors with plasmons / Franchini, Anna; Bortolani, Virginio; R. F., Wallis. - In: JOURNAL OF PHYSICS. CONDENSED MATTER. - ISSN 0953-8984. - STAMPA. - 16:(2004), pp. 4221-4232. [10.1088/0953-8984/16/24/004]