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We review our results on the growth of ZnTe-and CdTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by using molecular beam epitaxy (MBE) with the use of a mechanism of catalytically-enhanced growth. The growth of ZnTe, CdTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Cd, Mn, Mg and Te sources on the surfaces of (001)-, (110)-and (111)B-oriented GaAs substrates with Au nanocatalysts. The morphological and structural properties of the nanowires were assessed by using X-ray diffractometry, field-emission scanning electron microscopy, and high resolution transmission electron microscopy. Additional studies of the compositions of both the nanowires and the Au-rich nanocatalysts were performed with the use of energy dispersive X-ray spectroscopy. The optical properties of the NWs were assessed by using photoluminescence and Raman-scattering studies performed in both macro and micro modes. The studies revealed that binary and quaternary nanowires with average diameters from 30 to 70 nm and lengths from 1 to 2.6 µm were monocrystalline in their upper parts, their growth axis was 111 , and they grow along the [111] direction of the substrate, independent of the substrate orientation used. A Au-rich (with 20 % Ga) spherical nanocatalyst was always visible at the tip of a nanowire, thus indicating that a vapor-liquid-solid mechanism was responsible for the growth of the ZnTe-and the CdTe-based nanowires. The formation of homogeneous mixed crystal ZnMnTe and ZnMgTe nanowires was demonstrated by measurements of the variation of the lattice constant and by Raman experiments that revealed the expected shift and appearance of new phonon lines and a strong enhancement of the LO-phonon structures for an excitation close to the exciton energy of the NW materials. The photoluminescence from the internal Mn 2+ transition between crystal-field-split energy levels ( 4 T1 → 6 A1) was observed in the ZnMnTe nanowires.

We report on optical studies of exciton magnetic polarons in artificial crystals of digital alloys of diluted magnetic ͑semimagnetic͒ semiconductors built of alternating CdTe and Cd 1Ϫx Mn x Te layers, each only a few monolayers thick. Specially designed quantum well structures with the digital magnetic alloy in the quantum well region were grown and studied experimentally by magneto-optical methods. Precise comparative studies of the structures grown simultaneously either on ͑120͒or ͑100͒-oriented substrates were performed by photoluminescence excitation spectroscopy and photoluminescence under selective excitation. While no difference in magnetic properties, as measured by the giant Zeeman splitting of excitonic states, was observed between ͑120͒and ͑100͒-oriented diluted magnetic structures, the exciton magnetic polaron energy was found to be by 10-40 % larger in ͑120͒-oriented structures than in ͑100͒-oriented counterparts. This increase is explained by the effect of the heavy-hole effective mass anisotropy: greater hole mass in ͓120͔ direction causes an enhancement of an initial exciton localization which, in turn, gives rise to an increase of the magnetic polaron energy. Results of model calculations are in good agreement with experimental data. ͓S0163-1829͑98͒00432-9͔ PHYSICAL REVIEW B 15 AUGUST 1998-II VOLUME 58, NUMBER 8 PRB 58 0163-1829/98/58͑8͒/4785͑8͒/$15.00 4785

Collective excitations have been analyzed for Cd1-xMnxΤe epilayers (0.66 < x < 1) by the Raman scattering studies performed at temperatures frk 7 K to 295 K. Apart from the lattice opticał modes magnetic excitations (magnons) were observed at sufficiently low temperatures.PACS numbers: 75.30.Ds, 78.30.Fs Bulk zinc-blende crystals of Cd1-xMnxTe can be obtained by equilibrium growth techniques only for x < 0.7. For higher Mn contents the system crystallizes in hexagonal NiAs stucture. However, one can obtain Cd1-x Mn x Te for 0.7 < x < 1.0 in a metastable form with the zinc -blende stucture by MBE on substrates of the cubic symmetry. In this paper thin films of zinc-blende Cd1-x Mn x Te with 0.7 < x < 1.0 were grown using an EPI 620 MBE system on semi-insulating (001)GaAs wafers. A thin (100-1000 Å) ZnTe layer was employed in order to reduce the strong mismatch between a typical 2 μm thick CdTe buffer layer and GaAs substrate and to stabilize the growth in the (100) direction. A mixed crystal composition was determined by X-ray diffraction methods.Raman scattering experiments were performed in a quasi backscattering geometry. Spectra were recorded using a double monochromator equipped with holographic grating and a S20 photomultiplier or CCD detecting system. For the excitation Ar+ laser lines (457.9 nm, 476.5 nm and 514.5 nm) and Kr+ lines (647.1 nm and 530.9 nm) were applied. *Crystal growth is supported by the PΒΖ-Ζ011/P4/93/01 and 7Τ08Α04109 grants from the State Cominittee for Scientific Research (Republic of Poland).(941)

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