Optimisation of resonant tunnelling injection and doping density in high-performance THz superlattice quantum cascade lasers

This study attempts to reduce the fast increase of threshold current densities J/sub TH/ with temperature by optimising the performance of a recently demonstrated superlattice QCL emitting at /spl lambda/ = 100 /spl mu/m using different active region doping levels. In addition, this work studies the injection efficiency as a function of the thickness of the Al/sub 0.15/Ga/sub 0.85/As barrier controlling the tunnel coupling between the superlattice miniband and the upper state of the laser transition.