Growth of Fe/ZnSe Multilayers on GaAs (001) AND (111) by Molecular Beam Epitaxy
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few years.' Such systems often exhibit giant magnetoresistance (GMR), with potential for practical applications in magnetic recording. Several example systems include Co/Cu, Fe/Ag, and Fe/Cr superlattices. The coupling in these metallic systems is thought to be mediated by the conduction carriers in the non-magnetic metallic spacer layer. In a recent paper, Mattson et. al. 2 reported on the coupling of ferromagnetic Fe films separated by thin layers of Si. The authors reported that the coupling at low temperature changed from ferromagnetic to antiferromagnetic upon illumination of the sample with visible laser light. Other reports on similar systems indicate that the coupling was induced by thermal excitation. 3' 4 The prospect of extending magnetic interlayer coupling to include semiconductor spacer layers is exciting from both a scientific and a technological point of view. Such systems may allow the manipulation of the exchange coupling via the control of carrier densities in the spacer layer either by doping or by photo-excitation. The Fe/ZnSe system offers some advantages over the Fe/Si system in this regard. Since ZnSe is a direct wide bandgap semiconductor, photo-induced effects may be more readily manifested and easily distinguished from thermally induced effects. From a materials growth standpoint, the lattice match is more favorable, with the mismatch between ZnSe and twice the lattice constant of Fe being 1.1% compared to 5.5% for the Fe/Si system. In addition, 73 Mat. Res. Soc. Symp. Proc. Vol. 384 01995 Materials Research Society
extensive work has established that it is possible to grow Fe epilayers on ZnSe (001) with excellent magnetic and structural properties.5 Auger electron diffraction and x-ray photoelectron spectroscopy studies have shown that Fe grows on the 2x 1 reconstructed surface of ZnSe (001) in a layer-by -layer manner, with little interdiffusion or compound formation at the interface. 6 However, the growth of ZnSe on an Fe epilayer presents a new and different set of problems and is more challenging. The growth of a polar material on a non-polar one (e. g. the growth of GaAs or CdTe on Si) 7 is inherently difficult and can lead to structural defects such as antiphase domains. Although the optimum growth temperature of ZnSe on GaAs (001) is typically quoted as 300' C, a lower growth temperature for ZnSe on Fe is important to minimize interdiffusion at the ZnSe/Fe interface and to preserve the magnetic character of the Fe layer. Migration enhanced epitaxy (MEE) 8 allows the epitaxial growth of semiconductors at low temperatures and was utilized in the work reported to grow ZnSe epilayers on Fe. RESULTS AND DISCUSSION Details of the growth of ZnSe on Fe (001) films at low temperature (175' C) were reported recently. 9 To briefly summarize, in the present work all the ZnSe spacer layers were grown using migration enhanced epitaxy (MEE) 8 at 175° C. This method allows the growth to proceed at a low temperature compatible with the growth and preservation of the underlying Fe layer as well
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