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(a) Conduction and (b) valence band structures of one period of the active region 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. Beginning with the leftmost injection barrier, the layer thicknesses measured in nm are 2.5/1.7/1.0/4.6/1.0/4.3/2.0/3.2/1.1/3.0/1.1/2.9/1.2 . The numbers in bold refer to barrier layers. The underlined layers are doped to . The shaded areas show the injector minibands.
(a): PL spectra measured at different applied voltages: 0, 8.9, and , as marked on the current-voltage characteristics shown in the inset. The heat sink temperature is . The PL intensity in the range of has been multiplied by a factor of 5. (b) PL spectrum measured from the (001) surface of an unprocessed sample in which the whole sequence of InP upper layers and of the InGaAs upper cladding have been removed by wet etching. The energy ranges of the transitions and between the conduction and valence subbands, calculated by varying the chemical composition of the barrier and the conduction and valence band offsets by , are marked on the figures.
(a) Voltage dependence of the photoluminescence band, collected at the heat sink temperature . (b) Electrical power dependence of the lattice temperature (∎) and electronic temperature of the subband (●) measured in the center of the active region on the QCL front facet at . The lines are linear fits to the data. The extrapolated value of the temperature at is due to the heating induced by the probe laser. Inset: Electronic temperature increase as a function of the current density measured at . is the constant temperature shift due to the laser heating.
Experimental (symbols) and calculated (solid line) temperature profiles measured along the growth axis in the center of the QCL front facet driven by a cw electrical power of , at . The shaded area marks the active region layer.
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