Terahertz quantum-cascade laser at λ≈100 μm using metal waveguide for mode confinement

We report lasing at $\text{∼3.0\hspace{0.17em}}\mathrm{THz}$ $\text{(λ≈98–102\hspace{0.17em}μ}\mathrm{m})$ in a quantum-cascade structure in which mode confinement is provided by a double-sided metal waveguide. The depopulation mechanism is based on resonant phonon scattering, as in our previous work. Lasing takes place in pulsed mode up to a heat-sink temperature of 77 K. The waveguide consists of metallic films placed above and below the 10-μm-thick multiple-quantum-well gain region, which gives low losses and a modal confinement factor of nearly unity. Fabrication takes place via low-temperature metallic wafer bonding and subsequent substrate removal using selective etching. This type of waveguide is expected to be increasingly advantageous at even longer wavelengths.