Enhanced Surface Carrier Response by Field Overlapping in Metal Nanopatterned Semiconductor

Abstract

We demonstrate photoexcited carrier response of metallic nanogap-patterned semiconductor using optical pump-terahertz probe spectroscopy. Metallic nanogap facilitates observing surface carrier dynamics of bulk semiconductors by means of strong field confinement and enhancement of electromagnetic waves at nanoscale. Here, we observe that the enhanced terahertz transmission change of photoexcited InP has a nonmonotonic behavior (increases and then decreases) as reducing the gap size, which originates from different field confinement of near-infrared light (pump) and terahertz waves (probe). This 5 observation is theoretically reproduced by our simple model which informs that one can obtain the maximum pump probe signal at the condition in which the field overlapping of two different electromagnetic waves used in the pump probe experiment becomes maximized. Our results pave the way toward designing nanogap-based optical devices operated by multiwavelength electromagnetic waves.