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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).
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.
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 .
(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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