Taiichi Otsuji
RIEC - Tohoku University, Japan
Title: Single-mode terahertz lasing in current injection graphene channel transistor
Biography
Biography: Taiichi Otsuji
Abstract
Optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the terahertz (THz) spectral range, which may lead to new types of THz lasers. In the graphene structures with p-i-n junctions, the injected electrons and holes have relatively low energies compared with those in optical pumping, so that the effect of carrier cooling can be rather pronounced, providing a significant advantage of the injection pumping in realization of graphene THz lasers. We fabricated a distributed-feedback (DFB) dual-gate graphene-channel transistor as a current-injection terahertz laser. A pair of teeth-brash-shaped gate electrode was patterned to form a DFB cavity in which the active gain area and corresponding gain coefficient are spatially modulated. A single mode emission at 5.2 THz was observed at 100 K beyond the threshold carrier injection level. The single mode emission exhibits a non-monotonic threshold-like behavior with the highest intensity ~10 μW, reflecting the carrier over-cooling effect under weak pumping. Spectral narrowing with increasing the carrier injection around the threshold was also observed. The result is still preliminary level but the line width fairly agrees with calculation based on DFB-Fabry-Perrot hybrid-mode modeling.