Correlation between laser-induced hot-electron cooling and quantum efficiency in THz quantum cascade lasers

The authors will present an experimental study of the correlation of the electronic temperature of the active region with the stimulated emission of photons in QCLs. Using micro-probe photoluminescence (PL) the authors report the evidence of a new physical phenomenon characteristic of semiconductor lasers, i.e. the cooling of the electrons above the laser threshold for stimulated emission. This effect is directly related with the quantum efficiency, which is one of the central physical quantities in the theory of semiconductor lasers. As a model system we have selected the terahertz quantum cascade laser, in which hot-electron effects must be fully understood to explore the device physical limits in terms of maximum temperature, wavelength and quantum efficiencies.