Action of a Semiconducting Nanoshell: From Shielding to Plasma Resonance and Beyond

Space charge interactions in a semiconducting nanoshell are studied by a transport formulation for carrier dynamics and a quasi-static account for the polarizing electric field in the terahertz frequency range. Numerical results are obtained for the charge density, electric field intensity within and outside the shell and the total induced dipole moment. When the shell thickness is sufficiently large (compared to the screening length of the space charge), the shell behaves like a solid particle at lower frequencies. Above the plasmon resonance, the inertia effect of the charge carriers subdues their ability to respond instantaneously to the applied field so that their screening effect is diminished, giving rise to standing wave buildup in the shell and the electric field reaching the cavity region. Spectral response of the shell, as revealed by the real part of the dipole moment, shows a difference from that of a solid particle, provided that the photon energy is insufficient to activate transition across the energy bandgap of the semiconductor. The action of the nanoshell can be visualized as a high-pass filter in the coupling of a terahertz electric field to its interior cavity.