Direct observation of doping incorporation pathways in self-catalytic GaMnAs nanowires

Abstract

Publication date: 2015 Document VersionPublisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Kasama, T., Thuvander, M., Siusys, A., Gontard, L. C., Kovács, A., Yazdi, S., ... Sadowski, J. (2015) Doping mechanisms of Mn in GaAs nanowires (NWs) that have been grown self-catalytically at 600 C by molecular beam epitaxy (MBE) are investigated using advanced electron microscopy techniques and atom probe tomography. Mn is found to be incorporated primarily in the form of non-magnetic tetragonal Ga 0.82 Mn 0.18 nanocrystals in Ga catalyst droplets at the ends of the NWs, while trace amounts of Mn (22 6 4 at. ppm) are also distributed randomly in the NW bodies without forming clusters or precipitates. The nanocrystals are likely to form after switching off the reaction in the MBE chamber, since they are partially embedded in neck regions of the NWs. The Ga 0.82 Mn 0.18 nanocrystals and the low Mn concentration in the NW bodies are insufficient to induce a ferromagnetic phase transition, suggesting that it is difficult to have high Mn contents in GaAs even in 1-D NW growth via the vapor-liquid-solid process. V C 2015 AIP Publishing LLC.

Magnetic properties of wurtzite (Ga,Mn)As

“…Finally, the MBE growth of Mn-doped GaAs NWs at higher temperatures, optimized for GaAs NWs resulted in the very low Mn content, below 10 18 cm −3 [16,17]. Moreover, the accumulation of an excess Mn in the catalyzing droplets at the NW tops [17] or as Mn-rich (MnAs) nanocrystals at the NW sidewalls was evidenced [18].…”

“…Another method -Mn ion implantation to GaAs NWs grown at optimum high temperature also resulted in high density of structural defects and with no transition to FM phase [15]. Finally, the MBE growth of Mn-doped GaAs NWs at higher temperatures, optimized for GaAs NWs resulted in the very low Mn content, below 10 18 cm −3 [16,17]. Moreover, the accumulation of an excess Mn in the catalyzing droplets at the NW tops [17] or as Mn-rich (MnAs) nanocrystals at the NW sidewalls was evidenced [18].…”

Growth and properties of self‐catalyzed (In,Mn)As nanowires

“…Local distribution of spins in such nanostructures seems to be depended not only on their sizes, but also on their shape. This brings up many questions concerning the formation of nanostructures, especially nanowires and quantum dots based on so called diluted magnetic semiconductors (DMS). Unlike DMS layers, which grow usually at relatively low temperatures to avoid phase separations, nanostructures can be formed at higher temperature range .…”

“…Similar to thin films, the most attention has been paid to the study of the growth of the NWs based on (Ga,Mn)As DMS. They have been obtained using a variety of catalysts for the growth, such as MnAs , Ga , Mn , as well as by overgrowth of wrapped shell on GaAs NWs and by Mn ion implantation . It should be noted, that usually the formation of (Ga,Mn)As shell carries out at lower temperatures .…”

“…At the same time, the use of Ga or Mn assisted synthesis of (Ga,Mn)As NWs allows to increase the growth temperature and, as consequence, the crystalline quality of the structures. Nonetheless, for the NWs grown by Ga‐assisted molecular‐beam epitaxy (MBE), it was found that Mn atoms had been accumulated in the Ga droplet . Moreover, no significant incorporation of Mn atoms into the nanowire was observed , although residual doping level had not been determined.…”