Selective-area growth and magnetic characterization of MnAs/AlGaAs nanoclusters on insulating Al₂O₃ layers crystallized on Si(111) substrates

We report on selective-area metal-organic vapor phase epitaxy and magnetic characterization of coupled MnAs/AlGaAs nanoclusters formed on thin Al₂O₃ insulating layers crystallized on Si(111) substrates. Cross-sectional transmission electron microscopy reveals that poly-crystalline γ-Al₂O₃ grains are formed after an annealing treatment of the amorphous Al₂O₃ layers deposited by atomic layer deposition on Si(111) substrates. The ⟨111⟩ direction of the γ-Al₂O₃ grains tends to be oriented approximately parallel to the ⟨111⟩ direction of the Si substrate. We observe that hexagonal MnAs nanoclusters on AlGaAs buffer layers grown by selective-area metal-organic vapor phase epitaxy on partially SiO₂-masked Al₂O₃ insulator crystallized on Si(111) substrates are oriented with the c-axis along the ⟨111⟩ direction of the substrates, but exhibit a random in-plane orientation. A likely reason is the random orientation of the poly-crystalline γ-Al₂O₃ grains in the Al₂O₃ layer plane. Magnetic force microscopy studies at room temperature reveal that arrangements of coupled MnAs nanoclusters exhibit a complex magnetic domain structure. Such arrangements of coupled MnAs nanoclusters may also show magnetic random telegraph noise, i.e., jumps between two discrete resistance levels, in a certain temperature range, which can be explained by thermally activated changes of the complex magnetic structure of the nanocluster arrangements.