Polarization Enhancement and Resonance Tuning Inferred From Theoretical Consideration and Numerical Simulation for a Semiconductor Nanoparticle With a Dielectric Shell

Electric polarizations in metallic nanoparticles have enabled them to be employed in a variety of applications such as sensors, light trapping, polarizer, filter, and wave guiding at optical frequencies. Semiconductor nanoparticles, with a lower carrier concentration and hence plasma frequency, can be expected to find applications in the terahertz frequency range. The effect of a dielectric shell on the charge-field interaction in a semiconductor nanoparticle in the terahertz frequency range is investigated. The presence of a nonconductive layer on the surface of a conductive particle results in a modification in its polarization properties. Employing a formulation based on carrier transport in the semiconductor, the space charge dynamics is revealed, along with the electric field inside and outside the core-shell structure. From the polarizations, in the semiconductor and the dielectric, the total induced dipole moment is obtained. Building upon an equivalent circuit developed for the bare semiconductor nanoparticle, the equivalent circuit for the core-shell particle is arrived at. It provides a direct correspondence of the polarizability of the structure to the circuit elements, whose values are given in closed-form expressions in terms of the material parameters in the two regions. The process in the development of the equivalent circuit provides physical insight to the polarization within the structure, while the circuit obtained enables models for a cluster of interacting particles to be built by employing network theory.