High-Performance THz Quantum-Cascade Lasers

The THz frequency range (1-10 THz) falls in between two other ranges where semiconductor devices are well developed. One is the microwave and millimeter-wave frequency range, and the other is the near-infrared and optical frequency range. Semiconductor electronic devices (such as transistors) are limited by the transit time and parasitic RC time constants to below ~1 THz. Conventional semiconductor photonic or quantum electronic devices (such as laser diodes) are limited to frequencies above the semiconductor energy gap, which is higher than 10 THz.

In this project, we are developing semiconductor THz devices based on intersubband transition in quantum wells, which essentially are human-made 1D molecules. Based on two novel features: resonant-phonon THz gain medium and metal-metal waveguides, we have achieved many performance records. These include but not limited to: the highest operating temperature relative to the photon energy (by a factor of ~2), the highest pulsed operating temperature of 186 K, the first CW THz QCL operating above the important liquid nitrogen temperature of 77 K (Tmax = 117 K), and the highest power of ~250 mW in pulsed mode and ~130 mW cw.