Multilayer quantum dots were grown using SSMBE. Seed layer of InAs QD was grown over 1000Å intrinsic GaAs layer
on semi-insulating GaAs (001) substrate and capped with 30Å quaternary In0.21Al0.21Ga0.58As and 90Å intrinsic GaAs layer for samples A and B while for sample C it was 20Å and 80Å. Growth rate was 0.2011 ML/s for samples A and C whereas 0.094 ML/s for sample B. Each sample was annealed at 650°C, 700°C, 750°C and 800°C. Greater growth-rate produced more strain in samples A and C producing more dot families and for sample B these increased with annealing
because of the interdiffusion of constituents among the QDs. 750°C annealed samples A and C showed higher integrated
PL intensity and activation energy because carriers found lower minimum energy states for relaxation, attributed to
higher growth rate. In/Ga interdiffusion caused blue shift in photoluminescence(PL) spectra for samples B and C at
higher annealing temperatures whereas due to greater capping layer thickness almost no shift for sample A due to
intermixing of In-Al between the quaternary alloy and wetting layer, making it thermally stable. Decrease in FWHM due
to enhanced carrier relaxation is counterbalanced by non-resonant multi-phonon assisted tunneling processes, suggesting
good uniformity.
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