Masters defense: Charline Kaisa Reffeldt Kirchert

Selective Area Grown InAs QDs on GaAs buffer dot structures - Characterization and photo luminescence observation

For this thesis selective area (SAG) grown InAs QDs are grown on GaAs buffer dots tructures using electron beam lithography (EBL), HF wet etching and molecular beam epitaxy (MBE) growth techniques. The mask openings and GaAs buffer structures have been studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM), the GaAs/InAs interface and InAs QDs have been investigated using tunneling electron microscopy (TEM) and the photo luminescence (PL) of the InAs QDs have been observed using an above band excitation (ABB) laser.

The formation of shapes of the GaAs buffer are classified into 4 different growth stages; 1. 4-fold symmetry with facet family {110}{111}, 2. 4-fold symmetry with facet family {110}, 3. 1-fold symmetry with facet family {110}{111} and 4. 4-fold symmetry with facet family {111}. The nominal growth rate ΓInc, i.e how much material that have been Incorporated into the SAG openings compared to a thin film growth without a mask, have been found for the GaAs buffer dots to be of maximum 0.019, which indicate sourcing growth mode where more material is going to the mask then what is incorporated in the mask openings. The InAs QDs were found to be highly relaxed on top of the GaAsbuffer dots with a dislocation diameter of 8.6 nm - 10 nm and the diameter measured to roughly 70 nm and height to roughly 30 nm. This results in wavelengths approaching the wavelengths of bulk InAs (3000 nm). Wavelengths above 1100 nm were not possible to detect in the spectrometer available for this project however luminescence was seen in the camera for some of the QDs even though the efficiency above wavelengths of 1000nm for the camera were under 5 %.