COLLECTIVE EXCITATIONS IN N-I-P-I SUPERLATTICES - FINITE-SIZE EFFECTS

A theoretical investigation has been made of the collective (bulk and surface) excitations in a finite superlattice system consisting of n- and p-doped semiconductors separated by an intrinsic i semiconductor ( n-i-p-i superstructure). An implicit dispersion relation is derived em ploying the fully retarded theory in the framework of a transfer-matri x method. The plasmon-polariton modes are defined by the electromagnet ic fields localized at and decaying exponentially away from each inter face and from the ends of the superlattice system. Numerical examples are presented for two illustrative cases: (i) all the four layers of a unit cell being of equal thicknesses; and (ii) the thicknesses of n- and p- doped layers being half of the intrinsic layers. The numerical results correspond to an ideal system in which the damping effects are ignored and the semiconducting layers are modeled by real, local diel ectric functions. The propagation characteristics of plasmon polariton s and their inverse penetration depths have been studied. The conseque nces of reducing the size of the superstructure to a single unit cell have also been explored. The major attention has been focused on the c omparison of theoretical results for the finite superstructure with th ose for the semi-infinite and/or infinite superstructure.