Optical absorption cross section of quantum dots

Abstract

We have measured the modal optical absorption spectrum of a three-layer system ofInAs quantum dots in a slab waveguide geometry, observing distinct absorptionpeaks for the ground and excited states. The spectrally integrated absorptioncross section for the ground and first excited states are determined to beσ0 = (0.43 ± 0.1) × 10−15 and (0.92 ± 0.2) × 10−15 cm2 eV, respectively. Assuming that the spectral shapes are determined primarily by theinhomogeneous size distribution of dots the Gaussian linewidths are 16 and 19 meV for the groundand first excited state transitions, respectively. The peak ground state absorption cross section is1.1 × 10−14 cm2. The ground state spectrally integrated cross section estimated by atheory with the envelope function overlap integral taken to be unity is0.40 × 10−15 cm2 eV, in agreement with the measured value. We conclude that on the basis of the spectrallyintegrated cross section there is no evidence for a substantial reduction in the strength ofthe fundamental light–matter interaction in dots compared with systems of higherdimensionality.