The detailed cross-sectional structure of InGaAs quantum dots fabricated by a heterogeneous droplet epitaxy method was investigated by means of cross-sectional transmission electron microscopy observation. It was confirmed that concave disks without any dislocations or wetting layer were formed at the upper part of the flat surface. This result was consistent with the change of photoluminescence intensity and peak position. The sizes of the disks were estimated to be 30 and 12 nm in lateral and vertical directions, respectively. From this estimation, the occurrence of a phase-separation effect is suggested.
The fabrication of nanometer-scale GaAs dots on AlGaAs layer by molecular beam epitaxy was
demonstrated. Unlike the stress-driven transition of the three-dimensional growth mode in the
lattice-mismatched system, the limited migration of Ga droplets on the AlGaAs
layer grown at low substrate temperature was exploited to give rise to the formation of
three-dimensional GaAs islands. The resulting GaAs dots show crater-like features
having {111} facets. In micro-photoluminescence measurements of the
buried structures, the emission spectra were clearly observed, and the
sharp lines of the spectra might be considered as the exciton
emissions from individual dots with various sizes.
We report the direct formation of self-assembled GaAs/AlGaAs quantum dots by low-temperature molecular beam epitaxy. To drive a three dimensional growth mode, the (1ϫ1) AlGaAs surface was exposed alternately to the Ga and As sources. The resulting GaAs nanocrystals having ͕111͖ facets were clearly identified by high-resolution transmission electron microscopy. The emission spectra also confirmed the formation of dots. The transition to a three-dimensional growth mode is attributed to the limited surface migration of Ga adatoms on the AlGaAs surface, which has excess As at low substrate temperature.
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