Growth and characterization of In1−xMnxAs diluted magnetic semiconductors quantum dots

The growth of low-temperature In1−xMnxAs quantum dots (QD) on low-temperature GaAs(001) was investigated. Three different growth conditions with variable As2 flux, Mn:In flux ratio and QD layer thickness were studied by atomic force microscopy and transmission electron microscopy. All three conditions generated In1−xMnxAs QD with a cubic crystal structure. It is shown that an excess of As2 combined with a flux ratio of Mn:In=0.10 and a limited deposited thickness of 5.4ML In0.59Mn0.41As are the best conditions to obtain symmetric QD coherent to the substrate. Photoluminescence analysis performed on the latter samples showed a narrow band near 1100nm, indicating 3D-confinement of the dots. The magnetic properties of a multilayer of 5.4ML In0.59Mn0.41As QD were analyzed by magneto-optical Kerr effect at 1.6K. No magnetization could be detected, whereas measurements performed on a multilayer of 2.4ML In0.59Mn0.41As quantum wells indicated ferromagnetism. The absence of ferromagnetism for the QD is assigned to the superparamagnetism of the islands and the low Mn:In ratio used for the growth. It is suggested that these growth conditions are generating QD with a lower chance for interdot exchange interaction within a layer.