Collective excitations and their lineshapes for a compositional superlattice of type II

Abstract

The dielectric function and the density - density correlation function are calculated for a compositional superlattice of type II, which consists of alternate electron and hole layers (a two-component plasma) in an inhomogeneous dielectric background. The dielectric background of the electron gas is considered to be different from that of holes and the finite width of an electron (hole) layer is considered to allow both intrasubband and intersubband transitions. Our model superlattice consists of electron plasma, hole plasma, lattice vibrations of the background of the electron gas and lattice vibrations of the background of the hole gas. Electron - electron, electron - hole, hole - hole, electron - phonon, hole - phonon and phonon - phonon interactions take place in our model superlattice. Our calculation is applied to the superlattice. Variation of plasmon - phonon coupled modes and their lineshapes with (x, y) and unit cell width has been investigated in order to study the effects of semiconductor to semimetal or vice versa phase transitions. It is found that phase transition prominently affects the plasmon modes, while phonon modes remain almost unaffected. The inhomogeneity in the background of the electron - hole gas also produces a significant change in plasma frequencies. Lineshapes of coupled plasmon - phonon modes for both semimetal and semiconductor phases are calculated and are computed with those of the homogeneous background. Significant changes in peak height and half width are observed due to inhomogeneity in the dielectric background and the semiconductor to semimetal phase transition.