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Research & Reviews : Journal of Physics

Theoretical Study of UV Surface Waves in AlAs and AlN

  1. Arjun Mishra
  2. Daya Shanker

Abstract

Surface waves excited at the interface between polar semiconductor surface and a dielectric when electromagnetic waves of appropriate frequency are incident on it. When the incident electromagnetic energy in the form of photons is absorbed, these surface excitations generate. They are of different kinds such as plasmon, phonon, exciton etc. Plasmon is the quanta of valence electron oscillation; phonon is the quanta of lattice vibration and exciton is the quanta of electron-hole pair oscillation. When a photon is coupled with any of these excitations, polariton waves excite. So, they are also different types such as plasmon-polariton, phonon-polariton, exciton-polariton etc. Dispersion relation, obtained from Maxwell equations, helps to study these excitations. This relation gives frequency dependent dielectric function ε(ω) and for the existence of surface waves, this dielectric function ε(ω) must be negative. Here, planar interface between semiconductors (Aluminium Arsenide (AlAs) and Aluminium Nitride (AlN)) and vacuum is taken for the study of coupled optical phonon-plasmon surface oscillations. The ratio between incident frequency (ω) and plasmon frequency (ωp) is calculated for different values of dielectric function. Two coupling frequency modes(ω/ωp)+and (ω/ωp)− are obtained. For AluminiumArsenide (AlAs) and Aluminium Nitride (AlN), this surface wave exists when (ω/ωp)+less than 0.35 and (ω/ωp)+less than 0.46 respectively; as for this range, the dielectric function remains negative. These modes are obtained in the ultraviolet (UV) region (1016 Hz). The other (ω/ωp)− mode remains nearly constant with values 0.0033 and 0.0036 for AlAs and AlN respectively and found in Infrared (IR) region (1013 Hz). Study of these and other new materials with other geometries such as cylindrical, spherical etc. can give promising results. Nanotubes are cylindrical in shapes, so this method is useful to analyse them. The surface modes in different frequency ranges have great role and these findings have importance in the synthesis of modern sophisticated optical devices (light emitting diodes: LEDs, sensors, photodetectors etc.) and useful for different technologies.

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