Comparison of luminescence properties of bilayer and multilayer InAs/GaAs quantum dots

Coupled InAs/GaAs quantum dots have generated an interest for their longer emission wavelength and narrower line-width. However, a consensus has not been reached on the parameters of growth required to achieve a desired effect from coupling due to contradictory reports of shorter emission wavelengths. In this paper, we seek to compare the luminescence properties of bilayer quantum dots (BQDs) with those of multilayer quantum dots (MQDs), grown at a very low deposition rate, keeping all parameters constant. The BQD and MQD samples were grown by solid source MBE at a slow growth rate of 0.03 ML/s. A blueshift in the PL spectra for 11 layer coupled InAs/GaAs MQD heterostructure is observed compared to the BQDs for temperatures less than 180 K. This undesired blueshift is attributed to strain in the structure which overshadowed the usual redshift in emission wavelength in such structures due to electronic coupling. The variation in PL line-width with temperature in the MQD structure is found to be much lower than in the BQD. However the PL intensity of the MQDs fall at a faster rate with temperature compared to the BQD sample, due to strain generated non-radiative centers in the islands which favors in thermalization of carriers.