Plasmon-enhanced terahertz emission from a semiconductor/metal interface

Terahertz emission by ultrafast optical excitation of semiconductor/metal interfaces strongly depends on the strength of the depletion-field. Here, we report on the strong enhancement of the emission after optical excitation of surface plasmons at these interfaces. The enhancement is caused by the plasmonic localization of the pump light near the metal surface, where the depletion-field is the strongest. Compared to the case where no surface plasmons are excited, a terahertz field enhancement of more than an order of magnitude is obtained for a particular thickness of cuprous oxide layer on gold, where localized surface plasmons are excited at the interface.