Plasmonic Hot-Carriers in Channel-Coupled Nanogap Structure for Metal–Semiconductor Barrier Modulation and Spectral-Selective Plasmonic Monitoring

Plasmonic hot-carriers, which are induced by plasmons at metal surfaces, can be used to convert photon energy into excited carriers over a subwavelength region and provide a new means to realize photodetection within the sub-band-gap region of semiconductor materials. However, the barrier height of the metal–semiconductor junction affects the behavior of the plasmon-induced hot-carriers and limits the electrical response of photodetection. High electrical responsivity, achieved by manipulating the barrier height using plasmon-induced hot electrons, is desired to broaden the possible applications. Here we report a plasmonic channel-coupled nanogap structure, where the barrier height of the metal–semiconductor junction is altered upon the excitation of plasmon-induced hot-carriers. The structure consists of semiconductor channels and metal slabs forming nanogaps, which sustain coupled plasmons and confine light to the semiconductor–metal interfaces. In contrast to conventional Schottky barriers and ohmic contacts, in which plasmon-induced hot-carriers and the generation of electron–hole pairs by photoabsorption cause an increase in the photocurrent, the generation of plasmon-induced hot-carriers at the resonant wavelength results in an increase in the junction barrier height and a decrease in the photocurrent induced by photoabsorption. By modifying the barrier height, the plasmon resonance can be monitored from the electrical response with a high spectral resolution and a large modulation.