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  • The results we obtained are also in a

    2018-11-02

    The results we obtained are also in a good agreement with the photoconductivity spectra under excitation by p- or s-polarized light in a structure similar to the one we examined, also containing wide doped QWs [10], where a broad buy OF-1 line associated with the 1→e1 and 1→2 transitions was also observed. It can be seen from comparing the terahertz PL spectra obtained for the sample with wide doped QWs at two temperatures (see Fig. 3) that the intensity of terahertz PL decreases with the temperature increase. This may occur because the probability that an electron is trapped by the ionized donor also decreases. This behavior of terahertz luminescence with increasing temperature has already been observed in bulk semiconductors by the authors of Ref. [21]. To confirm the suggested mechanism of terahertz emission involving impurity states in QWs, we measured the interband PL spectrum (Fig. 4), the same as for the sample with the narrow QWs. The arrows in Fig. 4 indicate the spectral peculiarities which may be associated with radiative recombination of heavy-hole free excitons bound to the ground electron and hole subbands (the Xe1→hh1 transition in Fig. 4), as well as with radiative recombination of donor bound excitons (the Si→X transition in Fig. 4). The above-described spectral peculiarities were identified based on the experimental data and the calculation of the energy spectrum, and on comparing the estimations of the impurity and the exciton binding energies in the QWs. The broad emission band in the photon energy range from 1.48 to 1.51eV, marked as M (matrix), may be associated with the band→impurity optical transitions in the bulk layers of the structure. This band is also observed in the interband PL spectra for the structure with narrow doped QWs (see Fig. 2). The emission line at the photon energy of 1.528eV can be attributed to radiative recombination of nonequilibrium electrons and holes via the ground impurity state (the 1→hh1 transition in Fig. 4), since it differs from the calculated value of the e1→hh1 radiative transition by 8meV. This result is in a good agreement with the calculated electron energy spectrum taking into account the impurity states [10], as well as with the results of the analysis of terahertz PL spectra of the sample with wide QWs (see Fig. 3).
    Conclusion The study was supported by a RFBR grant no. 16-32-60085, a grant of the President of the Russian Federation for young Candidates of sciences MK-6064.2016.2, and by the Ministry of Education and Science of the Russian Federation (state assignment).
    Introduction This paper considers the processes associated with recombination of non-equilibrium charge carriers in nanostructures with InGaAsSb/AlGaAsSb quantum wells. There is much interest in studying these structures because it is possible to use them to fabricate sufficiently powerful semiconductor injection lasers with the wavelength range of 2–4µm, operating in continuous-wave mode. Lasers emitting in the mid-infrared (mid-IR) region can be widely applied in the fields of spectroscopy of various substances, transmission of information via wireless communication lines, in security and fire control systems, in medical, military and other industries. We should note that the transparency of the atmosphere in this spectral range [1] expands the range of applications for such lasers significantly. However, fabricating the sources in the wavelength range near 3µm has not been fully accomplished yet despite this problem\'s importance. Using unipolar quantum cascade lasers at wavelengths of about 3µm seems problematic because it is difficult to construct a semiconductor structure with significant band discontinuities between two semiconductor materials. The issue of creating lasers in this range can be approached from another perspective by extending the working range of InGaAsSb/AlGaAsSb injection lasers operating at wavelengths less than 2µm to longer wavelengths. However, it is known from experiments that an increase in emission wavelength results in increased lasing threshold current and decreased radiated power of injection lasers [2].