Calorimetric investigation of intersublevel transitions in charged quantum dots

Intersublevel transitions in InGaAs quantum dots (QD’s) are observed by means of midinfrared Fourier transform calorimetric absorption spectroscopy. This technique permits one to measure spectrally resolved the heating of a sample illuminated by a midinfrared radiation source. Thus, effectively a QD bolometer for the midinfrared energy range has been realized, allowing for sensitive absorption studies. Absorption peaks observed in the 70 to 110 meV range are attributed to electron intersublevel transitions based on a comparison to exciton properties derived from photoluminescence and photoluminescence-excitation measurements. For charge-tunable QD’s in a space charge region, the population of ground and excited electron sublevels can be changed by the applied reverse bias, allowing for an identification of the observed intersublevel transitions on the basis of their charging dependence. Charging-dependent energy shifts and intensity changes of the intersublevel absorption peaks are ascribed to few-particle effects and to Pauli blockade effects, respectively. The QD intersublevel absorption cross section is estimated to be of the order of ${10}^{-13}{\mathrm{cm}}^2,$ the according absorption coefficient is comparable to that of QD interband (exciton) transitions.