Growth mode and interface formation of Fe and Co films on ZnSe(001) (abstract)

Abstract

The incorporation of magnetic layers in semiconductor heterostructures is an increasingly active area of study. We are interested in the growth of ferromagnetic layers on diluted magnetic semiconductor (DMS) substrates as a means of magnetically polarizing the DMS medium, a necessary condition for these materials to exhibit the extraordinary magneto-optic and transport properties for which they are known. Since interfacial effects are expected to play an important role in thin-film heterostructures, we have examined the growth of Fe and Co films on ZnSe(001) to determine the mode of film growth, the formation of the interface, and the structure of the overlayer at the 1–10 monolayer level. The results obtained should apply to the growth of such overlayers on the ZnSe-based DMS compounds for modest magnetic ion concentrations as well, such as (Zn,Mn)Se, (Zn,Fe)Se, and (Zn,Co)Se. The ZnSe(001) samples were grown by molecular-beam epitaxy on GaAs(001) substrates, passivated with a Se coating in a manner analagous to the As passivation of GaAs, and transferred to a surface analysis system. The Se coating was thermally desorbed in UHV at 150–200 °C just prior to metal deposition. The metal films were deposited from miniature electron-beam sources and characterized in situ with Auger electron diffraction, RHEED, and x-ray photoelectron spectroscopy. The coverages were determined by x-ray flourescence measurements. The coverage dependence of the forward scattering peaks in the Auger electron diffraction scans due to the occupation of second and third monolayer sites provides information on the initial mode of film growth. The angular position of these peaks provides a measure of the out-of-plane lattice spacing, and hence the structure of the overlayer. We find that the growth of Fe(001) on a ZnSe(001) epilayer is predominantly 2D in nature at a substrate temperature of 175 °C, while growth directly on the oxide-desorbed GaAs(001) bulk substrate shows more significant 3D clustering. While the growth of Co on GaAs(001) results in a nearly ideal bcc single-crystal structure, growth on ZnSe(001) epilayers yields a multicrystalline structure. Little interaction with the ZnSe is observed with XPS.