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Calculated band structure at a field of of our samples. One cascade is marked with the box. The growth sequence in starting from the left is , where the barriers are marked bold and the doped well is underlined. The optical transition happens between the wave functions marked with 3, 4 (upper laser states), and 2 (lower laser state). The lower laser state is depopulated into the ground states , , and of the next cascade by a LO phonon. The inset shows a (dashed line) and a (dash-dotted line) of sample G951 at . The two kinks in the correspond to the alignment and the misalignment of the cascades.
Threshold current density (dashed line) and (dash-dotted line) at as a function of the sheet density. Both rise linearly with the doping concentration.
Field vs current density. All samples lase in a narrow field region, between 8 and . The inset shows a of a nominally undoped sample. This structure shows the similar alignment and misalignment of the cascades beginning at .
Doping concentration, threshold current density , and growth deviation obtained by x-ray diffraction analysis for all samples. The x-ray diffraction results of H011 show peak splitting.
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