Control of self-organized formation of magnetic element-rich nanowires in semiconductors and its device application

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As an example of the aggregation of a magnetic element in semiconductors, we have studied the aggregation of Cr in a II-VI magnetic semiconductor (Zn, Cr)Te. We have grown thin films of (Zn, Cr)Te doped with a donor impurity iodine (I) by molecular beam epitaxy (MBE) and have investigated how the Cr aggregation depends on the growth conditions by performing structural analyses using transmission electron microscope (TEM) and x-ray diffraction (XRD) on a series of samples grown under a systematic variation of the MBE growth conditions. As a result, we have found that the Cr aggregation changes depending on the average Cr composition in the crystal and the growth temperature. In particular, for a high average Cr composition, Cr atoms aggregate into precipitates of Cr_<1-δ>Te nanocrystals of hexagonal structure and the amount of the precipitation increases with the growth temperature.