For highly desired THz applications, we discuss the design and fabrication of THz quantum cascade lasers (QCLs) toward the high temperature and large average output power operations for the real applications with the relatively compact portable size cryogenic cooling systems. We describe the temperature performance parameters of THz QCLs and introduce the recent results of an indirect injection design scheme in the THz region and modulation height active structure design with different barriers and wells for the further design direction. The recent fabricated THz QCLs are combined with the liquid nitrogen (LN) cooling Dewar condenser to demonstrate the relatively compact THz source unit by QCLs. The different injection schemes in THz and barriers‐wells height design in the active region introduce one of the directions for the further high temperature and large output power operation of THz QCLs. The relatively compact size THz source unit with a cryogenic system demonstrates the THz QCLs for real applications with the milliwatt order average output operation near liquid nitrogen temperature.
Part of the book: Quantum Cascade Lasers