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[en] Quantum-confinement levels in a CdxHg1−xTe-based rectangular quantum well are calculated in the framework of the four-band Kane model taking into account mixing between the states of electrons and three types of holes (heavy, light, and spin-split holes). Comparison of the calculation results with experimental data on the photoluminescence of CdxHg1−xTe-based quantum wells suggests that optical transitions involving the conduction and light-hole bands are possibly observed in the spectra.
[en] Quantum well (QW) population effects are compared in III-nitride light emitters with different levels of polarity. We show that wider nonpolar active QWs are characterized by increased QW transparency current and a reduced differential optical gain which consequently increases the laser threshold. We also show that high intra-QW recombination rates in nonpolar/semipolar structures make the QW populations strongly non-equilibrium and vulnerable to inhomogeneous QW injection. In the LED regime, structures with a different polarity level reveal different mechanisms of the efficiency droop. In polar structures, the droop is dominated by the electron leakage and is notably affected by the active region ballistic overshoot. The efficiency droop in semipolar/nonpolar structures is dominated by the combined effect of radiative time saturation and non-radiative Auger recombination
[en] A novel surface-emitting superluminescent diode (SLD) having a round active region surrounded by a circular grating is theoretically investigated. When the superluminescent light produced in the active region transmits to the passive region, it is coupled out of the device by the detuned circular grating, forming a symmetric surface-emitting beam that could not be obtained from previous devices. The calculation of the grating shows that a reflectivity below 10−3 can be achieved and is low enough to avoid lasing. Performances of devices using single and double quantum wells in the active regions have been simulated, which confirms feasibility of the new design, but also shows that the proposed SLD is unsuitable for high-power applications because of its relatively short length of gain compared to common stripe devices
[en] The coupling effects of quantum wells on band structure are numerically investigated by using the Matlab programming language. In a one dimensional finite quantum well with the potential barrier V_0, the calculation is performed by increasing the number of inserted barriers with the same height V_b, and by, respectively, varying the thickness ratio of separated wells to inserted barriers and the height ratio of V_b to V_0. Our calculations show that coupling is strongly influenced by the above parameters of the inserted barriers and wells. When these variables change, the width of the energy bands and gaps can be tuned. Our investigation shows that it is possible for quantum wells to achieve the desired width of the bands and gaps. (paper)
[en] The results of studying edge-emitting quantum-well lasers with a layered design having coupled planar waveguides, capable of suppressing the generation of excited transverse modes, are presented. In this case, a low internal loss (0.4 cm–1) is provided, combined with a small depth (~0.9 μm) of the active region, which results in a low thermal resistance of 6.0 (K/W) mm without a submount.
[en] Full text: We have recently demonstrated comb operation of a mid-infrared quantum cascade lasers. This presentation will report on new progress towards the realization of a dual-comb spectrometer as well as on the realization of very broadband (covering close to an octave in frequency) THz QCL active regions. (author)
[en] The circular photogalvanic effect and the circular photon drag effect are observed and investigated in detail in (110)-grown quantum well structures. The experimental data are well described by phenomenological theory and microscopic models of both effects are developed being in agreement with experimental data