Growth Direction Control of Ferromagnetic MnAs Grown by Selective-Area Metal–Organic Vapor Phase Epitaxy

Abstract

We report the position-controlled formation and the growth direction control of MnAs nanoclusters (NCs) on partially SiO2-masked GaAs (111)B substrates by selective-area metal–organic vapor phase epitaxy (SA-MOVPE). At a relatively low growth temperature of 750 °C, MnAs NCs were grown not only in the opening regions of SiO2 mask patterns but on SiO2 mask surfaces. The average density of unintentional nanoprecipitates deposited on SiO2 mask surfaces decreased with increasing V/Mn ratio of the supplied source gases. At a relatively high growth temperature of 850 °C, MnAs NCs were selectively grown in the opening regions of the SiO2 mask patterns. The MnAs NCs with well-defined crystal facets had the hexagonal NiAs-type crystal structure. The top and the six sidewall facets were attributable to {0001} and {1011} as determined by cross-sectional transmission electron microscopy and electron beam diffraction measurements. It was confirmed that the c-axis, <0001>, of the MnAs NCs was parallel to the <111>B directions of zinc-blend-type GaAs layers. The growth rate of crystal facets of the NCs was well-controlled by adjusting V/Mn ratio for MnAs growth. Magnetic force microscopy of NCs revealed that the NCs showed ferromagnetism at room temperature. Some of the MnAs NCs behaved as nanomagnets with a single magnetic domain.