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Notes: Abstract We report optical measurements (photoluminescence, Raman scattering, and infrared reflectance) of direct band gap and of optical phonon energies of BexZn1−x Se alloys grown by MBE on (001) GaAs substrates for a wide range of Be concentrations. The high band gap of BeSe (5.15 eV) suggests the possibility of using isoternary alloys for ultraviolet optoelectronic applications. BexZn1−x Se has the unique advantage that it can be lattice matched to Si at about x=0.5. We observed a strong linear shift of the BexZn1−x Se direct band gap to higher energies with increasing Be content (to 3.63 eV for x=0.34). Furthermore, optical phonon parameters for the entire range of BeSe content have been obtained. Finally, polarized infrared and Raman spectra revealed local atomic ordering (anti-clustering) effects in the group-II sublattice.

Notes: We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on the common structural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVI alloys in the absence of an external magnetic field, stressing the close relationship of the sp electron bands in these materials to the band structure of the nonmagnetic AIIBVI "parent'' semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half-filled Mn 3d5 shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of the magnetic properties of the AII1−xMnxBVI alloys. In particular, we discuss the mechanism of the Mn++-Mn++ exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susceptibility of DMS in the paramagnetic range; we describe a somewhat empirical picture of the spin-glasslike freezing in the AII1−xMnxBVI alloys, and its relationship to the short range antiferromagnetic order revealed by neutron scattering; and we point out some not yet fully understood questions concerning spin dynamics inDMS revealed by electron paramagnetic resonance. We then discuss the sp-d exchange interaction between the sp band electrons of the AII1−xMnxBVI alloy and the 3d5 electrons associated with the Mn atoms. Here we present a general formulation of the exchange problem, followed by the most representative examples of its physical consequences, such as the giant Faraday rotation, the magnetic-field-induced metal-to-insulator transition in DMS, and the properties of the bound magnetic polaron. Next, we give considerable attention to the extremely exciting physics of quantum wells and superlattices involving DMS. We begin by describing the properties of the two-dimensional gas existing at a DMS interface. We then briefly describe the current status of the AII1−xMnxBVI layers and superlattices (systems already successfully grown; methods of preparation; and basic nonmagnetic properties of the layered structures). We then describe new features observed in the magnetic behavior of the quasi-two-dimensional ultrathin DMS layers; and we discuss the exciting possibilities which the sp-d exchange interaction offers in the quantum-well situation. Finally, we list a number of topics which involve DMS but which have not been explicitly covered in this review such as elastic properties of DMS, DMS-based devices, and the emerging work on diluted magnetic semiconductors other than the AII1−xMnxBVI alloys—and we provide relevant literature references to these omitted topics.

Notes: We have measured the dependence of the indices of refraction n on alloy composition of Zn1−x−yMgxCdySe films grown by molecular beam epitaxy on InP substrates for a series of alloy compositions x and y. The compositions of the Zn1−x−yMgxCdySe thin films were determined by photoluminescence and x-ray diffraction experiments. A prism coupler technique, capable of measuring n with an accuracy of at least 0.1% at discrete wavelengths, was then used to measure n of each of the thin films. In all of the samples, at least three guided modes were observed in the spectrum obtained by the prism coupler method. The accurate values of n obtained by this method show an inverse relationship with respect to their band gaps. In addition, by comparing the n values obtained for the quaternary Zn1−x−yMgxCdySe alloys with the previously obtained values for the ternary Zn1−xCdxSe and Zn1−xMgxSe alloys, it is concluded that n of the quaternary system is almost completely dictated by the content of Mg. © 2001 American Institute of Physics.

Notes: We have investigated the epitaxial growth of Zn1−x CdxSe epilayers and ZnSe/Zn1−x CdxSe superlattices (0≤x≤1) on (100)GaAs. Although thick epilayers of Zn1−x CdxSe are prone to defect formation with increasing Cd content, the structural and optical characteristics improve remarkably when Zn1−x CdxSe is in the form of thin layers within ZnSe/Zn1−x CdxSe superlattices. High quality superlattices can be grown for x≤0.35. The characterization of these systems using transmission electron microscopy, x-ray diffraction, reflectivity, and photoluminescence is reported.

Notes: The nature of magnetic excitations in disordered and short-range ordered antiferromagnetic systems continues to be an interesting problem. The family of AII1−xMnxBVI alloys (AII=Zn, Cd, Hg, BVI=S, Se, Te) offers highly interesting prototypes for such studies. In these systems, which crystallize in the zinc blende (ZB) or wurtzite structure, the Mn ions form, respectively, diluted FCC or HCP Heisenberg spin lattices with dominating nearest-neighbor AF coupling. Due to the strong frustration inherent in such lattices these systems do not exhibit long-range spin order even for Mn concentrations as high as x=0.70. Neutron scattering studies of spin dynamics in the zinc-blende forms (Zn1−xMnxTe and Cd1−xMnxTe) have been reported in a recent article.1 In the present paper we report the results of experiments on a wurtzite-type system, Zn1−xMnxSe, with x=0.55 and 0.40. As in the previous case of ZB alloys, the data reveal the existence of magnon-like modes that are extremely strongly damped, but still show a pronounced dispersive behavior. The range of static AF spin–spin correlations in Zn1−xMnxSe is extremely short (ξ=κ−1=5–15 A(ring)), and exhibits a significant anisotropy. The energy of the observed excitation is clearly correlated with ξ, i.e., it is higher in the Q-space directions for which the correlation range is longer. The results are discussed in the context of the existing theoretical models.

Notes: Far-infrared magnetotransmission experiments were carried out on two Hg1−xCdxTe superlattices with graded composition grown by laser molecular beam epitaxy. A superlattice k⋅p model was used to calculate the subband structures of the superlattices. Good agreement is found between the experimental results and the theory if the valence-band offset is assumed to be small.

Notes: We report the growth of cubic (zinc blende) CdSe epilayers on [100] GaAs substrates by molecular beam epitaxy. The lattice constant of the CdSe epilayers is 6.077 A(ring), and the energy gap is 1.75, 1.74, and 1.67 at 10, 80, and 300 K, respectively.

Notes: The FCC Heisenberg spin lattice with AF NN interactions is a known model of an inherently frustrated system. Due to the continuous ground state degeneracy, the spin order in this lattice is particularly sensitive to weak symmetry-breaking perturbations, such as Dzyaloshinski–Moriya (D-M) interactions or anisotropic strains. These effects may create a rich variety of colinear and noncolinear structures. The limited availability of naturally existing prototypes has resulted in little experimental work in this field. However, the emergence of novel epitaxial structures containing zinc-blende type MnSe and MnTe, which are very close approximations of the NN FCC Heisenberg model, opens new opportunities for such studies. In many of these systems the MnSe and MnTe layers are strongly strained (c/a∼0.95–1.05) due to lattice mismatch effects. The resulting anisotropy in the Mn-Mn exchange may lead to a dramatic change in the spin structure—e.g., studies of MnSe/ZnTe superlattice systems have revealed a transition from a type III AF order to an entirely new incommensurate helical state not yet seen in any FCC aniferromagnet.1 In this paper we report neutron diffraction data from "thick'' (∼1 μm) Co0.25Mn0.75Se films. Detailed mapping of the magnetic diffraction intensity reveals a shift from perfect type III lattice points, showing that detectable incommensurate effects may be produced even by weak residual stresses. Our results point out that noncolinear effects arising from strains may be indistinguishable from canting produced by D-M exchange,2 which may additionally complicate the detection of this weak interaction in Mn chalcogenides.

Notes: Results of Shubnikov–de Haas (SdH), cyclotron resonance (CR), and Hall-effect measurements on δ-doped InSb:Si films grown by molecular-beam epitaxy on insulating InP substrates are reported. The investigation covers samples with sheet densities of Si dopant atoms ranging from 1×1011 to 1×1013 cm−2, temperatures from 4.2 to 300 K, and fields from 0 to 7 T. The SdH oscillations show that the samples contain electrons of two-dimensional nature, occupying multiple subbands. The effective masses obtained from the CR data correspond well to the subband occupation densities. The Hall measurements as well as the CR experiments also give evidence for the presence of additional electrons, with the conduction-band-edge mass m*=0.014m0 of bulk InSb, which exist presumably in the bulk of the films.

Notes: The index of refraction of Cd0.9Mn0.1Te was measured at a wavelength of 10.25 μm at room temperature on twinned unoriented monocrystal samples. The result was n=2.57±0.01. Furthermore, the temperature dependence of the index of refraction was measured to be (1/n)dn/dt=5.0±0.1×10−5 K−1. The optical absorption coefficient was α=0.13 cm−1. Finally, the linear expansion coefficient in the range of 293–373 K was found to be γ=−1±1×10−6 K−1. © 1995 American Institute of Physics.