Terahertz microcavity lasers with subwavelength mode volumes and thresholds in the milliampere range

The authors demonstrate terahertz microcavity lasers with ultralow current thresholds (Ith≈4mA) and with reduced mode volumes of ≈0.7(λeffective)3, i.e., less than one cubic wavelength. A double metal waveguide with reduced active core thickness (5.82μm) is used to achieve confinement in the vertical direction, without compromising the laser performances. Confinement in the longitudinal direction is obtained using microdisk resonators. The guiding properties of surface plasmons are exploited to guide the mode with the metal contact. This makes the use of a resonator with vertical and smooth sidewalls unnecessary. The emission wavelength is λ≈114μm. The devices lase up to 70K in pulsed mode, and they achieve continuous-wave operation up to 60K.