AVS 47th International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI+EL-WeM

Paper MI+EL-WeM6
Properties of Mn@sub x@Ge@sub 1-x@, Cr@sub y@Ge@sub 1-y@ and Mn@sub x@Cr@sub y@Ge@sub 1-x-y@ Semiconductor Films Grown by Molecular Beam Epitaxy@footnote 1@

Wednesday, October 4, 2000, 10:00 am, Room 206

Session: Magnetic Semiconductors and Hybrid Structures I
Presenter: J.E. Mattson, Naval Research Laboratory
Authors: J.E. Mattson, Naval Research Laboratory
Y.D. Park, Naval Research Laboratory
T.F. Ambrose, Naval Research Laboratory
A.T. Hanbicki, Naval Research Laboratory
A. Wilson, Naval Research Laboratory
G. Spanos, Naval Research Laboratory
B.T. Jonker, Naval Research Laboratory
Correspondent: Click to Email
Mn doped GaAs exhibits ferromagnetic ordering along with semiconducting behavior.@footnote 2,3@ Recent theory@footnote 4@ suggests that low concentrations of Mn (<5%) in other semiconductor compounds should result in ferromagnetic behavior at high hole concentrations (p >10@super 20@ cm@super -3@). We describe here the structural, magneto-transport, and magnetic properties of Ge@sub 1-x@Mn@sub x@, Ge@sub 1-y@Cr@sub y@ and Ge@sub 1-y-x@Cr@sub y@Mn@sub x@ thin films (with x < 0.15, and y < 0.15) in which Mn and Cr act as acceptors. Samples were grown by MBE on GaAs(001) and Si(001) substrates at substrate temperatures ranging from 175 to 350°C and growth rates of 4-5 Å/min. For all growth conditions studied, the GeMn films show a largely diffuse RHEED pattern and lack of structural order as determined by XRD. The temperature dependence of the resistivity shows non-metallic behavior with room temperature hole concentrations as high as 3x10@super 20@cm@super -3@. The magnetic properties determined from SQUID magnetometry are similar to those of Ge@sub 8@Mn@sub 11@ bulk alloys, suggesting the formation clusters of Ge@sub 8@Mn@sub 11@ rather than a homogeneous alloy. Plan-view TEM confirms the presence of clusters. The GeCr films exhibit single crystal growth and are p-type with p<10@super21@cm.@super -3@ They are paramagnetic, however, with no evidence of any bulk ferromagnetic GeCr phases. In contrast, the GeCrMn films show a ferromagnetic transition below 70K which can not be correlated with a bulk phase, are strongly p-type with p ~10@super 21@ cm,@super -3@ and exhibit non-metallic temperature dependent resistivity. Additional results will be presented and discussed in the context of recent theory. @FootnoteText@ @footnote 1@ This work supported by ONR and the DARPA SPINS program. @footnote 2@H. Ohno, J. Magn. Magn. Mater. 200, 110 (1999)@footnote 3@H. Shimizu, et al., Appl. Phys. Let. 74, 398 (1999)@footnote 4@T. Dietl, et al., Science 287, 1019 (2000).