Differential absorption spectroscopy on coupled InGaAs quantum dots

Abstract

We report on the electroluminescence (EL) spectra and the differential absorption (Δ α) spectra for triple-layer InGaAs quantum dots (QDs) of different GaAs spacer thicknesses. Cross-sectional transmission electron microscopy directly reveals that the InGaAs QDs of 5-nm spacer are well-aligned along the growth direction. The Δ α spectra exhibit an increase of absorption change as the spacer layer thickness decreases from 40 to 5 nm. Meanwhile, the amount of absorption change at the photon energy of the excited transition becomes higher than that of the ground-state transition for the QDs of spacer thickness less than 20 nm. The Δ α results are consistent with the EL spectra showing the higher emission intensity for the excited transition. From the EL and Δ α experiments, the higher optical gain and absorption change for the excited transition suggest that the e2–h2 transition has higher oscillator strength for the vertically coupled QDs.