Photoluminescence and photothermal deflection spectroscopy of InAs quantum dot superlattices grown on GaAs by molecular beam epitaxy

In this report, we apply simultaneously the measurements of luminescence and absorption to InAs/GaAs quantum dot superlattices grown on GaAs substrates. It is found that the peak energy obtained by a radiative process increases with decreasing dot size due to the effect of quantum confinement. Because the size of the quantum dots that we studied is significantly larger than that of dots in previous reports, we are able to justify the theoretical calculation of the transition energy in InAs dots grown by molecular beam epitaxy. A highly sensitive technique of photothermal deflection spectroscopy (PDS) is used as the absorption technique. We show that PDS is more than sufficient to measure optical absorption in thicknesses of a few atomic layers. The obtained band-gap energies for different sizes of InAs quantum dots can be predicted accurately by the quantum confinement effect and agree well with the results of photoluminescence measurements. We demonstrated that PDS is an alternative tool for the study of nano-structure devices.