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22 February 2006 Non equilibrium electrons in THz quantum cascade lasers
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We compare the electrical power dependence of the lattice temperature and the electronic temperature of THz quantum cascade lasers (QCLs) operating in the range 2.5- 3.8 THz and based on a resonant-phonon and bound-to-continnum quantum design. This analysis is performed by means of microprobe band-to-band photoluminescence experiments carried out on operating THz QCLs both below and above the lasing threshold. Thermalized non-equilibrium hot-electron distributions are found in both classes of QCLs. While in the case of bound-to-continuum devices a unique value of the electronic temperature is found in the active region minibands, in the case of resonant-phonon devices we found that the upper radiative state, in the lasing range, heats up to ~ 200 K, more than 100 K with respect to the ground state levels. From the measured thermal resistance and the power dependence of the ground state electronic temperature we obtain in the case of resonant-phonon structures a value of the electron-lattice energy relaxation rate comparable with that typical of mid-infrared QCLs, in the case of resonant-phonon structures and a value ~ 50 times higher in bound-to-continuum devices.
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Miriam Serena Vitiello, Gaetano Scamarcio, and Vincenzo Spagnolo "Non equilibrium electrons in THz quantum cascade lasers", Proc. SPIE 6133, Novel In-Plane Semiconductor Lasers V, 61330K (22 February 2006);

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