Abstract

Terahertz Quantum Cascade Lasers (QCLs) are complex heterostructure devices, where lasing action occurs between electronic levels in the conduction band only — in other words, they are unipolar lasers. The levels are carefully designed and carried out by growing hundreds of nanometre-thick GaAs/AlGaAs wells/barriers in an MBE chamber. The wafers are subsequently fabricated into 200μm ridges and embedded in an unusual “surface plasmon” waveguide — this is necessary in order to confine radiation in sub-wavelength dimensions, at the expense of high free carrier loss. After 10 years of development, QCLs remain one of the best THz sources: they are compact, tunable and reliable.

I will briefly describe the principle of operation of QCLs, their design and fabrication. Then I will move on to talk about loss mechanisms, which are a limiting factor in the temperature performance of the lasers. I will propose a way of reducing losses by changing the waveguide geometry; I will show preliminary simulation results and discuss fabrication challenges for the proposed design.