| Quantum cascade lasers (QCLs) is a promising high output power semiconductor THz sources to realize the compact size THz application. The most important recent issue today is the limited operation temperature around 200 K and the operation frequency from 1.2 to 5.2 THz. Here we demonstrate a high injection selectively indirect injection diagonal emission design; realize the top level low frequency (< 2 THz) high temperature operation THz QCLs at 1.9 THz up to 160 K; introduce a new design idea of modulation barrier-well height structure in order to improve the temperature performance by the AlGaAs/GaAs THz QCLs. And we also successfully demonstrated the first lasing action emitting at the high frequency (5.5 THz) THz QCLs by the AlGaN/GaN THz QCLs. |