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(a) Conduction band structure of one period of the active region calculated using a self-consistent Schrödinger–Poisson solver with a voltage drop of per period, corresponding to the laser threshold. Starting from the injection barrier, the layer thickness in nanometers are (from right to left): . Values in bold correspond to layers. The underlined GaAs wells are -doped to . The wavefunction square moduli of the upper and lower laser levels are labeled as 8 and 6, respectively, while those of the injector doublet are marked as 1,2. The shaded areas identify the active region and injector subsystems. (b) Representative PL spectra measured in a wide- long QCL at the current densities (1), (2), (3), (4), each plotted as a function of the energy difference with respect to the corresponding energy of the low energy peak of the doublet. The vertical lines, labeled and mark transition energies between conduction and valence subbands. The heat sink temperature is .
[(a)–(c)] Mean lattice temperature (◼) and electronic temperatures (●); (▲) of (a) a wide- long QCL and (c) a wide- long QCL measured as a function of the electrical power at . increases linearly with with slopes (a) and (c) larger than the thermal resistances (a) , (c) . The shaded areas mark the lasing regions while the dashed vertical lines identify the transition between regions I and II. [(b)–(d)] Voltage-power and differential resistance vs power characteristics collected at , in continuous wave mode.
Difference between the electronic temperatures of the active region and the lattice temperature measured as a function of the electrical power at in a wide- long QCL (◼) and in a wide- long mesa device (▲).
[(a)–(d)] Difference between the electronic temperatures of the active region and the lattice temperature measured as a function of in the device active region of a wide- long QCL at temperatures (a) , (b) , (c) , and (d) . The shaded areas mark the lasing regions. (e) Internal quantum efficiency and (f) maximum wall-plug efficiency plotted as a function of the heat sink temperature measured in a wide- long QCL. The symbols (◼) in panel (f) represent the total maximum wall-plug efficiency values extracted from the measurement of the optical power. A collection efficiency value of is estimated from the comparison.
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