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 (T_max = 117 K), and the highest power of ~250 mW in pulsed mode and ~130 mW cw.

Selected publications:

• B. S. Williams, H. Callebaut, S. Kumar, Q. Hu, and J. L. Reno, “3.4-THz quantum cascade laser based on LO-phonon scattering for depopulation,” Appl. Phys, Lett. 82, 1015 (2003). [PDF]

• B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum cascade laser at lambda ≈ 100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83, 2124 (2003). [PDF]

• B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Optics Express, 13, 3331-3339 (2005). [PDF]

• B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “High-power terahertz quantum-cascade lasers,” Elect. Lett. 42, 89 (2006). [PDF]

• S. Kumar, Q. Hu, and J. L. Reno, “186 K operation of THz quantum cascade lasers based on a diagonal design,” Appl. Phys. Lett. 94, 131105 (2009). [PDF]

• S. Kumar, C. W. I. Chan, Q. Hu, and J. L. Reno, “A 1.8 THz quantum-cascade laser operating up to 163 K; significantly above the temperature of ,” Nature Physics 7, 166-171 (2011). [PDF]

• S. Fathololoumi, E. Dupont, C.W.I. Chan, Z.R. Wasilewski, S.R. Laframboise, D. Ban, A. Mátyás, C. Jirauschek, Q. Hu, and H.C. Liu, “Terahertz quantum cascade lasers operating up to ~200 K with optimized oscillator strength and improved injection tunneling,” Optics Express, 20, 3866 (2012). [PDF]
• Rudra Sankar Dhar, Seyed Ghasem Razavipour, Emmanuel Dupont, Chao Xu, Sylvain Laframboise, Zbig Wasilewski, Qing Hu, Dayan Ban, “Direct Nanoscale Imaging of Evolving Electric Field Domains in Quantum Structures,” Scientific Report, 4, 7183 (2014). [PDF]
• Asaf Albo and Qing Hu, “Investigating temperature degradation in THz quantum cascade lasers by examination of temperature dependence of output power,” Appl. Phys. Lett. 106, 131108 (2015). [PDF]
• Asaf Albo and Qing Hu, “Carrier leakage into the continuum in diagonal GaAs/Al_0.15GaAs terahertz quantum cascade lasers, Appl. Phys. Lett. 107, 241101 (2015). [PDF]
• Asaf Albo, Qing Hu, and John L. Reno, “Room temperature negative differential resistance in terahertz quantum cascade laser structures,” Appl. Phys. Lett. 109, 081102 (2016). [PDF]
• Asaf Albo, Yuri V. Flores, Qing Hu, and John L. Reno, “Two-well terahertz quantum cascade lasers with suppressed carrier leakage,” Appl. Phys. Lett. 111, 111107 (2017). [PDF]

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 (T_max = 117 K), and the highest power of ~250 mW in pulsed mode and ~130 mW cw.

Selected publications:

• B. S. Williams, H. Callebaut, S. Kumar, Q. Hu, and J. L. Reno, “3.4-THz quantum cascade laser based on LO-phonon scattering for depopulation,” Appl. Phys, Lett. 82, 1015 (2003). [PDF]

• B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, “Terahertz quantum cascade laser at lambda ≈ 100 µm using metal waveguide for mode confinement,” Appl. Phys. Lett. 83, 2124 (2003). [PDF]

• B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode,” Optics Express, 13, 3331-3339 (2005). [PDF]

• B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “High-power terahertz quantum-cascade lasers,” Elect. Lett. 42, 89 (2006). [PDF]

• S. Kumar, Q. Hu, and J. L. Reno, “186 K operation of THz quantum cascade lasers based on a diagonal design,” Appl. Phys. Lett. 94, 131105 (2009). [PDF]

• S. Kumar, C. W. I. Chan, Q. Hu, and J. L. Reno, “A 1.8 THz quantum-cascade laser operating up to 163 K; significantly above the temperature of ,” Nature Physics 7, 166-171 (2011). [PDF]

• S. Fathololoumi, E. Dupont, C.W.I. Chan, Z.R. Wasilewski, S.R. Laframboise, D. Ban, A. Mátyás, C. Jirauschek, Q. Hu, and H.C. Liu, “Terahertz quantum cascade lasers operating up to ~200 K with optimized oscillator strength and improved injection tunneling,” Optics Express, 20, 3866 (2012). [PDF]
• Rudra Sankar Dhar, Seyed Ghasem Razavipour, Emmanuel Dupont, Chao Xu, Sylvain Laframboise, Zbig Wasilewski, Qing Hu, Dayan Ban, “Direct Nanoscale Imaging of Evolving Electric Field Domains in Quantum Structures,” Scientific Report, 4, 7183 (2014). [PDF]
• Asaf Albo and Qing Hu, “Investigating temperature degradation in THz quantum cascade lasers by examination of temperature dependence of output power,” Appl. Phys. Lett. 106, 131108 (2015). [PDF]
• Asaf Albo and Qing Hu, “Carrier leakage into the continuum in diagonal GaAs/Al_0.15GaAs terahertz quantum cascade lasers, Appl. Phys. Lett. 107, 241101 (2015). [PDF]
• Asaf Albo, Qing Hu, and John L. Reno, “Room temperature negative differential resistance in terahertz quantum cascade laser structures,” Appl. Phys. Lett. 109, 081102 (2016). [PDF]
• Asaf Albo, Yuri V. Flores, Qing Hu, and John L. Reno, “Two-well terahertz quantum cascade lasers with suppressed carrier leakage,” Appl. Phys. Lett. 111, 111107 (2017). [PDF]