Midinfrared absorption ofPbSe/Pb1−xEuxTe<

Abstract

The midinfrared absorption of highly ordered self-assembled PbSe/Pb 1Ϫx Eu x Te quantum dot superlattices is investigated. A different approach is used for quantitative determination of the absorption spectrum of the dot superlattice by inserting it into a high-finesse microcavity structure with a small mode spacing and Pb 1Ϫx Eu x Te/EuTe Bragg mirrors. For such microcavities, we show a linear relation between the width of each cavity resonance and the extinction coefficient at the resonance energy. Thus, the absorption spectrum is experimentally determined from the resonance widths. It reveals a narrow peak arising from the quantum dots and a step from the two-dimensional wetting layers. The peak absorption coefficient of the dot ensemble amounts to 2.5ϫ10 4 cm Ϫ1 and is similar to that of the wetting layers. We also present calculations of the dispersion of the absorption coefficient based on model dielectric functions of quantum dots and wetting layers. From a fit to the experimental absorption spectrum, we deduce interband transition energies as well as corresponding oscillator strengths and level broadenings. The broadening of the dot transition due to dot size fluctuations of the large quantum dot ensemble is only 8.7 meV, confirming the exceptionally high dot size uniformity in the PbSe quantum dot superlattice.

Analysis of reflectance and modulation spectroscopic lineshapes in optoelectronic device structures

“…We have also measured and simulated similar CM width enhancements, when the relative CM and QW energies are varied by heating, instead of changing u [34]. A comparable effect has been exploited to measure the absorption of quantum dots within high-finesse microcavities, where the CM width is measured for different high-order cavity modes [35], rather than at different u or temperatures.…”

High temperature operation of 760 nm vertical-cavity surface-emitting lasers investigated using photomodulated reflectance wafer measurements and temperature-dependent device studies

“…This phenomenon has been The arrows indicate the temperature and wavelength at which the two points cross observed previously for a similar VCSEL [12] and has also been exploited by another group as a method for measuring the absorption of quantum dot superlattices placed within high-finesse microcavities. [13] The effect may well prove useful as a corroborative measurement to PR for monitoring when the CM is in tune with a QW transition.…”