Measurement of subband electronic temperatures and population inversion in THz quantum-cascade lasers

Vitiello, Miriam S.; Scamarcio, Gaetano; Spagnolo, Vincenzo; Williams, Benjamin S.; Kumar, Sushil; Hu, Qing; Reno, John L.
March 2005
Applied Physics Letters;3/14/2005, Vol. 86 Issue 11, p111115
Academic Journal
We compare the electronic temperatures and the population inversion both below and above the lasing threshold in three quantum-cascade lasers (QCLs) operating at 2.8 THz, 3.2 THz, and 3.8 THz using microprobe band-to-band photoluminescence. In the lasing range, while the ground-state temperature remains close to the lattice one (90 K–100 K), the upper radiative state heats up to ∼200 K. From the measured thermal resistance and the power dependence of the ground-state electronic temperature, we get a value of the electron-lattice energy relaxation rate comparable with that typical of midinfrared QCLs.


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