Columnar-shaped InAs/GaAs self-assembled quantum dots grown by molecular beam epitaxy

S-K mode In As islands were stacked closely by molecular beam epitaxy using thin GaAs intermediate layers. The intermediate layer thickness was reduced to 3 monolayer. We found that the stacked islands grew successfully even on such thin intermediate layers, but the amount of InAs supply for the stacked island formations had to be optimized. Cross-sectional transmission electron microscopy showed that the stacked islands grew aligning vertically on the first layer islands, and the structures, as a whole, were columnar shape. A sharp photoluminescence spectrum was obtained even at room temperature. The spectrum width reached about 42 meV. We fabricated double heterostructure lasers using these quantum dots (QDs). A threshold current density of 160 A/cm² (80 A/cm² per single QD sheet) was achieved under continuous-wave conditions at 25°C.