Nonmetallic Materials for Plasmonic Hot Carrier Excitation

Abstract

Optical excitation of hot carriers in metals can be achieved even with low energy photons. When a metal comes in contact with a semiconductor, carrier injection can take place from the metal to the semiconductor even with photons possessing sub-bandgap energies. While such internal photoemission has several decades of history, recent advances in plasmonics have brought the study of internal photoemission into a new era. The efficiency of hot carrier excitation can be improved drastically by rationally fabricating a metallic nanostructure to excite plasmon resonances. Moreover, the heating caused by the relaxation of plasmonic hot carriers is highly localized. These plasmon enhanced photoelectric and photothermal conversions have been studied intensively from fundamental and application-oriented viewpoints, wherein gold and silver have been exclusively used. By contrast, this progress report covers nonmetallic materials that can be used for plasmon enhanced photoelectric and photothermal conversions. The main nonmetallic materials covered herein are transition metal nitrides, transition metal carbides, and metal oxides. Although research on nonmetallic materials for photoelectric and photothermal conversions is in the preliminary stage, some nonmetallic materials have been shown to outperform gold. This progress report aims to highlight the recent progress and discuss future research directions.