The terahertz (THz) spectral range offers promising applications in science, industry, and military. THz penetration
through nonconductors (fabrics, wood, plastic) enables a more efficient way of performing security checks (for example
at airports), as illegal drugs and explosives could be detected. Being a non-ionizing radiation, THz radiation is
environment-friendly enabling a safer analysis environment than conventional X-ray based techniques. However, the
lack of a compact room temperature THz laser source greatly hinders mass deployment of THz systems in security check
points and medical centers. In the past decade, tremendous development has been made in GaAs/AlGaAs based THz
Quantum Cascade Laser (QCLs), with maximum operating temperatures close to 200 K (without magnetic field).
However, higher temperature operation is severely limited by a small LO-phonon energy (~ 36 meV) in this material
system. With a much larger LO-phonon energy of ~ 90 meV, III-Nitrides are promising candidates for room temperature
THz lasers. However, realizing high quality material for GaN-based intersubband devices presents a significant
challenge. Advances with this approach will be presented. Alternatively, recent demonstration of InP based mid-infrared
QCLs with extremely high peak power of 120 W at room temperature opens up the possibility of producing high power
THz emission with difference frequency generation through two mid-infrared wavelengths.