Optical features of InAs quantum dots-in-a-well structures

Electronic energy structure and features of optical interband transitions of InAs quantum dots-in-a-well structures are studied via photoreflectance (PR) and temperature-dependent photoluminescence (PL) spectroscopy. InAs dots were grown with and without InGaAs capping layer and embedded in GaAs/AlAs quantum wells. Experimental results revealed that the 5 nm thick InGaAs capping layer significantly improves PR and PL signal intensity. Moreover, a shift of the quantum dot ground-state optical transition to lower energy by about 120 meV was observed. The red-shift of the ground-state transition is associated mainly with an increase of dot size and decrease of strain within quantum dots. Furthermore, the origin of PL intensity quenching with temperature is discussed in terms of electronic energy structure revealed from PR spectra and calculations performed within effective mass approximation.