Transmission electron microscope study of InGaAs quantum dots fabricated by SPEED method

The structure of InGaAs: quantum dots (QDs) fabricated by; separated-phase enhanced epitaxy with droplets (SPEED) method was investigated by means of cross-sectional transmission electron microscopy. (TEM). No wetting layer w as observed between tile QDs, which indicate that the SPEED method was not based on the S-K mode. It was found that the lattice spacing of tile uncapp ed QDs was elongated in the vertical direction rather than in the lateral d irection because the QDs were buried in the flat surface of tile specimen w ith their top surfaces exposed to the air. After tilt growth uf capping lay er, the lattice spacing in the vertical direction shrank due to the compres sive strain of a GaAs capping layer, resulting in the formation of highly s trained QDs. This result is consistent with our previous speculation deduce d from photoluminescence measurements.