Coupling of two-dimensional and surface plasmons at selectively-doped semiconductor heterostructures

At a selectively-doped semiconductor heterostructure, two-dimensional (2D) plasmons at the heterojunction are coupled with surface plasmons of the semi-infinite electron system in the doped substrate. Assuming a sharply localized free-electron gas formed at the heterojunction, we demonstrate that this coupling plays an important role in electronic excitations at the heterostructure. In view of observation by high-resolution electron energy loss spectroscopy, we calculate the dynamical response of the coupled 2D and semi-infinite electron systems near the surface to the oscillatory external potential acting on the surface. We investigate the dispersion relation and the coupling structure of coupled modes, and the variation of the energy-loss intensity and the mode character along each dispersion branch.