3d Transition Metals in II-VI Semiconductors
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3d TRANSITION METALS IN II-VI SEMICONDUCTORS D. HEIMAN, M. DAHL, X. WANG, P.A. WOLFF, P. BECLA, A. PETROU*, and A. MYCIELSKI** MIT Francis Bitter National Magnet Lab, Cambridge, MA 02139, *Physics Department, SUNY Buffalo, NY 14260 "**Institute of Solid State Physics, Polish Academy of Science, Warsaw
ABSTRACT The magnetic and electronic properties of some I-VI semiconductors with 3d transition metals other than Mn are presented. For example, the nonzero orbital moment in Fe2 ' leads to more complex electronic energy levels than for Mnt ions. In (CdFe)Se, inelastic light scattering experiments demonstrate that the ground state is nonmagnetic (Van Vleck ion), and directly measures the energy spacing between the three lowest levels. For Sc2 * ions the donor level lies above the bottom of the conduction band in the Cd-based materials. INTRODUCTION Research on 11-VI semiconductors with Mn" has been quite productive in the past ten years in establishing many of the basic interactions. This is due to the simplicity of both the electronic and magnetic properties of the Mn' ion. On the other hand, most of the other 3d transition metals are more complex, leading to new effects not found with Mn2 ÷ ions. A striking example is the charge ordering of ionized Fe' donors in (Hg,Fe)Se.[1,2] Here, we will address some new effects and applications of non-Mn 3d transition metals in 11-VI semiconductors. Since Mn2÷ is the only magnetic 3d ion having a simple spin-only moment (S=5/2,
L=O), its paramagnetic properties are easy to model. In more concentrated material the d-d exchange interaction between the ions significantly modifies the magnetic properties. The mechanisms and effects associated with the d-d exchange have been relatively easy to understand because of the simplicity of the Mn2 ÷ ion. Figure 1 displays the quantum
numbers for spin (S) and orbital momentum (L) for all the 3d transition metal series. The nonzero orbital moment of all the non-Mn ions leads to more complicated magnetic behavior due to spin-orbit coupling in crystals. This coupling induces a nonmagnetic singlet ground state (Van Vleck ion) for the Fe2 ion. In addition to the magnetic properties, the energy levels of the 3d transition metals have some interesting interactions. The Mn2÷ donor level (2+/3+) lies deep within the valence band of all the 1I-VI semiconductors, shown in Fig. 2. In contrast to Mn2 , the
donor levels of other 3d ions often lie near the band edges, or even above the conduction band level. Thus some of these ions act as a source of large concentrations of conduction electrons, as with Fe in HgSe. One can also speculate that the transitions 2+ -+ 3+ might
be useful for optical processes, since the donor levels provide an additional level to interact with the existing conduction and valence band states.
Mat. Res. Soc. Symp. Proc. Vol. 161. c1990 Materials Research Society
480
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