MICROSCOPIC PHASE-STABILITY OF THE DILUTE MAGNETIC SEMICONDUCTOR CD1-XFEXSE

The solubility of Fe in CdSe crystal has been studied in detail in the past. Using powder diffraction and atomic absorption spectroscopy, it was concluded that the upper limit for the solubility of iron in CdSe is 12-15%, and the actual Fe concentration in a solid solution agrees with the nominal Fe concentration (calculated from the concentration of the reactants). In the present study this question is re-examined u sing techniques that probe the average properties of the solid solutio n, such as x-ray diffraction, and techniques that probe the local stru cture and composition of the solid solution on the micron scale, such as energy and wavelength x-ray dispersive microprobe analysis. It is s hown that the solubility of Fe in the CdSe matrix is appreciably small er than the nominal value, and that microsegregation is obtained at a much lower Fe concentration than previously concluded. The immiscibili ty of Fe in this matrix is consistent with the large deviation of the lattice constants from Vegard's law. It is attributed to the large str ain exerted on the lattice upon substitution of Cd by the much smaller Fe ion.