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Extremely high -values of long-wavelength , low-threshold-current-density quantum-cascade lasers based on the indirect pump scheme
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View: Figures


Image of FIG. 1.
FIG. 1.

Conduction band diagram and moduli squared of the relevant wave functions in the designed active region of the long-wavelength IDP QC laser. The lattice-matched layer sequence of one period of the active layers in angstroms starting from the injection barrier (toward the right side) is as follows: 33/39/27/35/5/68/6/66/8/60/17/52/13/48/15/ /20/43/22/42 where barrier layers are in bold, QW layers in roman, and doped layers are underlined. The bias field is assumed to be 30 kV/cm, high enough to align the ground state, and level of the previous injector to level 4 of the active region.

Image of FIG. 2.
FIG. 2.

Current-light output characteristics of a long-wavelength 4-mm-long IDP QC laser with HR-coated rear facet at different temperatures, 77–390 K. The output intensities at room temperature were calibrated by a thermopile detector. The current-voltage characteristic and the lasing spectra are also shown.

Image of FIG. 3.
FIG. 3.

Semilogarithmic plots of the threshold-current-densities of the long-wavelength IDP QC laser, and wavelength IDP and QC lasers as functions of heat-sink temperature. The characteristic temperatures, were deduced by the empirical exponential function, . The linear plots of the threshold-current-densities are also shown in the inset.

Image of FIG. 4.
FIG. 4.

Computed normalized electron-population in an injector and -value defined as of active regions of an IDP and DP QC laser as functions of the normalized pump-current-density, without stimulated emissions. In the computation, Eq. (3) of Ref. 7 for the IDP laser and the corresponding relation for the DP laser were used by assuming realistic numerical values, indicated in the interpretation of the band diagram (Fig. 1), for relaxation times and by taking account of their temperature dependences. For the IDP laser, point A is chosen to represent the threshold-current-density at 400 K that is almost equal to the maximum current-density as in the real IDP device shown in Fig. 2. For the DP laser, point C corresponds to the threshold-current-density, at 400 K, which is substantially lower than the maximum current density, , as in the wavelength DP device. The vertical distances between points A and B and between points C and D are determined by for the postulated change rate, and .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Extremely high T0-values (∼450 K) of long-wavelength (∼15 μm), low-threshold-current-density quantum-cascade lasers based on the indirect pump scheme