MBE growth and characterization of self-assembled InAs/GaAs quantum dot structures for infrared detection

In the scope of this thesis, single and multi-layered InAs/GaAs quantum dot structures have been grown and characterized. The growth kinetics of quantum dots have been investigated through a set of samples having different growth parameters for the purpose of clear and well-defined energy levels in the photoluminescence (PL) spectra. Single-layered samples whose growth conditions, particularly the amount of material and the growth temperature, are systematically changed have been grown. By use of different techniques, primarily the PL, the density, distribution, size of the quantum dots have been determined. The inferences on the size and distribution drawn from the PL technique by determining the energy levels of the quantum dots have been confirmed with other techniques. The most homogeneous quantum dot size distribution was obtained from the sample grown with 0.11 ML/s at 490 °C for the InAs amount of 2.5 ML. The re-optimization of the growth conditions was required to obtain the quantum dots having similar properties when the growth rate was changed to 0.14 ML/s. The formation of the quantum dots that are smaller in size and having similar size distribution have been obtained at 505 °C growth temperature for the same material amount (2.5 ML). Additionally, the tunability of the energy levels by post-growth thermal treatment has been demonstrated. Multi-layered infrared detector structures having different number of InAs QD active layers were grown. PL, spectral photoresponse and dark current measurements have been performed once the devices were fabrication. It has been shown that the dark current in the fabricated photodiodes was reduced and the photoresponse spectra were improved as the number of the layers are increased. It has been observed from the photodiodes annealed at different temperatures after their growth to tune the spectral detection range that the photoresponse spectra was shifted towards lower energy region and the dark current was reduced.