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


Image of FIG. 1.
FIG. 1.

Conduction (a) and valence (b) band structures of Sample a calculated with a voltage drop of per stage using a self-consistent method based on the iterative solution of the Schrödinger and Poisson coupled equations. A 66% conduction-band offset is used. Beginning with the left-most injection barrier, the layer thicknesses measured in Å are . The underlined layer is doped at that corresponds to a sheet density of . The energy levels are labeled using increasing integers starting from the ground state either in the conduction or valence bands. (c) Current density vs voltage characteristic of Sample a measured at the heat sink temperature of . The shaded area shows the lasing region. The right axis shows the electrical power (P).

Image of FIG. 2.
FIG. 2.

Representative PL spectra of sample (a) at different electrical powers, each plotted as a function of the energy difference with respect to the corresponding main peak energy . The heat sink temperature is . The dashed vertical lines labeled mark the energies of the transitions between levels in the conduction and valence bands [see Figs. 1(a) and 1(b)]. Inset: Main peak energy as a function of the electrical power. The line is a guide for the eyes.

Image of FIG. 3.
FIG. 3.

Dashed line: PL spectrum at . Solid line: Calculated PL components peaked at the theoretical energies of relevant transition [see Figs. 1(a) and 1(b)]. The low-energy side of each curve is a Lorentzian with half width at half maximum. The high-energy side is an exponential decay function .

Image of FIG. 4.
FIG. 4.

(a): Mean lattice temperature (∎) and electronic temperatures ; ,; in the active region of Sample a measured as a function of the electrical power at a heat sink temperature of . The lines are linear fits to the data. The small difference between and at zero-electrical power is a well known effect due to the heating of the electronic ensemble induced by the probe laser. (b) Relative populations between the upper and lower laser level as a function of the dissipated electrical power calculated for Sample a. The shaded areas mark the lasing region.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Measurement of subband electronic temperatures and population inversion in THz quantum-cascade lasers