Recent Developments in II-VI Diluted Magnetic Semiconductors
- PDF / 1,173,920 Bytes
- 9 Pages / 420.48 x 639 pts Page_size
- 108 Downloads / 339 Views
RECENT DEVELOPMENTS IN 11-VI DILUTED MAGNETIC SEMICONDUCTORS N. SAMARTH AND J. K. FURDYNA
Department of Physics, University of Notre Dame, Notre Dame, IN 46556. ABSTRACT Much of the work in diluted magnetic semiconductors (DMS) in past years has focused on the AV.MnxBw alloys such as CdixMnxTe. Recently, there has been an increasing accent on DMS alloys containing the transition metal ions Fe 2+ and Co2+. We review here the properties of these new materials and compare them with the Aýl_ MnxBvl alloys. We also examine the novel opportunities afforded by the molecular beam epitaxy of epilayers and heterostructures containing the "metastable" zinc-blende phase of Cdl.xMnxSe. INTRODUCTION The term "diluted magnetic semiconductor" (DMS) was originally coined to describe alloys such as Cdl.xMnxTe in which Mn2+ ions are randomly substituted for the group IHatoms in a II-VI semiconductor [1]. However, this nomenclature has grown to include diverse systems derived from other semiconductors (such as IV-VI's) and incorporating other magnetic ions (such as Co2+, Fe2 + and Eu 2+)[2]. Moreover, the non-equilibrium technique of molecular beam epitaxy (MBE) has enabled the growth of DMS materials not readily accessible to bulk growth, such as zinc-blende phases of MnSe [3], MnTe [4], FeSe [5] and CdlxMnxSe [6], as well as a new class of DMS alloys derived from III-V semiconductors [7]. In this paper, we review the properties of some of the new II-VI materials, beginning with the AxFexBVlalloys. We then discuss the new AI'xCoxBv' alloys (Znl-xCoxSe, Znl-xCoxS and CdlxCoxSe), followed by a look at the opportunities provided by the epitaxial growth of zinc-blende Cdl.xMnxSe, and conclude with a look at future prospects.
AV FexBV DMS ALLOYS As shown in Table I, the AI.IxFexBv" alloys grown to date include both wide-gap materials (Zni-xFexSe [8,9] and CdtxFexSe [10]), as well as narrow-gap alloys (Hgl-xFexSe [11, 12] and Hgl-xFexTe [13]). The alloy Hgl-xFexSe is of great interest due to the unique relationship between the Fe2 + level and the bottom of the conduction band of HgSe. Since the properties of this alloy have been extensively reviewed elsewhere [11, 12], we shall omit this material in the present review. The ground state of Fe 2+ is a non-degenerate Al orbital singlet that has no permanent magnetic moment. At high temperatures, there is sufficient contribution from excited states with a finite moment so as to give paramagnetic behavior with S - 2.1 [10]. The values of the nearestneighbor d-d exchange integral J as deduced from the Curie-Weiss behavior of the high temperature static susceptibility are comparable to those in the corresponding A~l.IxMnxBvl alloys -- see Table I. At low temperatures, the non-magnetic ground state of Fe 2÷ results in Van Vleck paramagnetism, as opposed to the Brillouin paramagnetic behavior of the A- xMnxB1 alloys. This was first demonstrated in studies of Hgl-xFexTe [13], and also later inferred from studies of Cdl.xFexSe [10] and Znl-xFexSe [8,9].
Mat. Res. Soc. Symp. Proc. Vol. 161. @1990 M
Data Loading...
