Size Quantization in InAs/GaAs Self-Assembled Quantum Dots Grown by Gas-Source Molecular Beam Epitaxy

The number of confined states in a self-assembled quantum dot (SAD) is determined by its size, shape and composition. By employing a gas-source molecular beam epitaxy, the average size of InAs self-assembled islands on the GaAs (001) surface was controlled by the InAs growth temperature. Meanwhile, indium segregation during the GaAs cap-layer growth was found to greatly modify the shape and actual composition of InAs/GaAs SADs resulting in a blue-shift in the ground state energy. By suppressing indium segregation, InAs/GaAs SADs 39 nm, 29 nm, 22 nm and 15 nm in their average diameters were obtained. The corresponding number of confined states observed was five, three, two and one, respectively. The energy separation between the states is about 50 meV, it does not change appreciably with decreasing the dot size but reduces with intensifying indium segregation.