K. Matsubara

Epitaxial growth of Cd1−xMnxTe films by ionized‐cluster beams and their magneto‐optical properties

Epitaxial growth of Cd1−xMnxTe films with x ranging from 0 to 0.76 has been investigated on sapphire (0001) substrates using the ionized‐cluster beam method. Magneto‐optical properties of the films are discussed using Kramers–Kronig relation. Epitaxial films in the form of a single crystal can be obtained at low substrate temperatures up to 300u2009°C by the reactive composing of an accelerated CdTe cluster beam and a neutral MnTe cluster beam. When CdTe clusters are only ionized and accelerated, the composition of grown films varies largely, depending on the acceleration voltage. Faraday rotation for Cd1−xMnxTe films represents a band‐edge dispersion, and the intensity increases as Mn concentration x increases; for the film with x=0.76, the maximum value of the Verdet constant was 0.72u2009°/cm G, which was two orders of magnitude larger than that of a CdTe (x=0) film. The magneto‐optical figure of merit θF/α (H=5 kOe) for a Cd1−xMnxTe (x=0.76) epitaxial film was estimated to be about 400u2009° at 660 nm.

Electron paramagnetic resonance of defects in β‐iron disilicide ceramics

The point defects in β‐iron disilicide ceramics, which may influence the thermoelectric properties of the ceramics, have been investigated by electron paramagnetic resonance (EPR). The 77‐K EPR spectra are dependent upon the Si/Fe ratio of the ceramics specimens. Several S=1/2 centers with g factors of about 2.0 are observed in both silicon‐deficient p‐type and iron‐deficient n‐type specimens prepared by sintering and subsequent annealing of FeSix(1.9<x<2.8) grains. These centers disappear in a specimen prepared by directly annealing a lump of FeSi2 alloy without sintering. By considering the difference of the sample‐preparation procedures, we conclude that the S=1/2 centers exist in the oxidized intergrain region of the ceramics. An S=1/2 signal with an anisotropic g factor (g1=2.061, g2=2.047, g3=2.024) arises only in iron‐deficient n‐type specimens. This signal is attributable to unionized donor electrons. A multiplet signal with zero‐field splitting arises in nearly stoichiometric p‐type specimens. Th...

Magneto-optical Kerr effect of rf-sputtered PtMnSb thin films

Thin films of the C1b‐phase Heusler alloy PtMnSb, prepared by rf sputtering and subsequent annealing, have been studied in order to assess the high magneto‐optical Kerr effect of this compound. The room‐temperature saturation magnetization (Ms) and coercive force (Hc) for PtMnSb thin films after being annealed at 500u2009°C were about 400 emu/cm3 and 110 Oe, respectively. The easy axis of magnetization was parallel to the film plane for all films. The polar Kerr rotation θK for the PtMnSb films with a C1b phase has a maximum value in excess of 1.8° at 710‐nm wavelength in a 5‐kOe external magnetic field perpendicular to the film plane. Thin films substituted with Ni for Pt, which are an admixture of PtMnSb and an isoelectronic compound NiMnSb, are also examined. The θK peak showed a red shift, in contrast with PtMnSb containing excess Pt concentration, where a blue shift was observed. The intensity reduced significantly with increasing Ni concentration in the films.

POINT DEFECTS AND THERMOELECTRIC PROPERTIES OF IRON DISILICIDE CERAMICS SINTERED WITH SIH4-PLASMA-PROCESSED MICROGRAINS

The point defects in β‐iron disilicide (β‐FeSi2) have been investigated by electron paramagnetic resonance (EPR) along with the thermoelectric properties. The samples used are FeSix (1.9≤x≤2.8) ceramics sintered with FeSix micrograins processed in SiH4‐plasma and nonprocessed. EPR detects (1) several S=1/2 signals and (2) a multiplet signal. An S=1/2 signal with orthorhombic g factors (g1=2.061, g2=2.047, g3=2.024) is detected in all n‐type specimens, and ascribed to unpaired electrons of donors associated with iron vacancies. The other S=1/2 signals are detected in both n‐type and p‐type specimens. The centers responsible for these signals are considered to exist in an oxidized intergrain region of the ceramics. The EPR intensity of the multiplet signal due to the closed‐pair of a high spin Fe3+ ion (S=5/2) and an S=1/2 center is reduced by SiH4‐plasma treatments. SiH4‐plasma processing of FeSix micrograins prior to sintering changes the Seebeck coefficient sign and magnitude, depending upon the conditio...

Epitaxial growth of zincblende MnTe films as a new magneto-optical material

Abstract Epitaxial films of MnTe with a zincblende structure have been successfully grown on GaAs (100) and sapphire (0001) substrates using the ionized-cluster beam deposition technique. The values of the lattice constant, 6.34 A, and the optical band gap, 2.92 eV (300 K), reveal that the MnTe films obtained have the previously hypothetical zincblende MnTe structure. In the Faraday rotation spectrum of the zincblende MnTe film, a large dispersion is observed near the band gap energy, and the peak value of the Verdet constant is about 0.6 deg/cm·G. From the X-ray photoelectron spectroscopy and the intra-Mn absorption, we investigate the Mn3d states of zincblende MnTe.

Ionized-cluster beam epitaxy of CdTe and its application to CdTe/PbTe multilayer structure

Abstract CdTe films and CdTe/PbTe multilayered structures have been grown on Si(111) and InSb(111) substrates by ionized-cluster beam (ICB) epitaxy. The crystal properties of CdTe films are studied, and it was found that they are of good crystallinity and effective as a buffer layer for CdTe/PbTe multilayered structures. The formation of the multilayered structures was confirmed by Rutherford backscattering measurements. Also, optical absorption measurements and the theoretical calculations revealed the existence of an n = 1 miniband in the potential well of the structure. The ICB technique has several unique features for film formation, and it was found to have a high potential for preparing functional thin films and devices.

Electro‐optical effects of Cd1−xMnxTe films prepared by ionized‐cluster beams

We report the first investigation of electro‐optical properties of Cd1−xMnxTe films, prepared by the ionized‐cluster beam deposition technique. Measurements of the birefringence Δn of the films were performed under applied electric field in the wavelength region from 800 to 450 nm. Major results obtained are as follows: The value of Δn rises to second power against the applied electric field, and for a film with x=0.77 a large quadratic electro‐optical coefficient of 3.5×10−12 cm2/V2 is obtained at 633 nm. The wavelength dispersion of Δn is observed near its band gap, suggesting that the electro‐optical properties of these films are caused by the Franz–Keldysh effect.

Faraday Effects Due to Excitons in Cd 1-x Mn x Te Films

The authors performed a theoretical investigation of the Faraday effect in Cd 1-x Mn x Te epitaxial films prepared by the ionized-cluster beam deposition technique. Splitting energies and oscillator strengths of an exciton level are calculated by taking account of a nondegenerate second-order perturbation. The wavelength dispersion of the calculated Faraday rotation spectra is compared with experimental data for Cd 1-x Mn x Te films. The results suggest that the Faraday rotation is closely related to the magneto-optical transitions to Zeeman splitting levels of excitons.

Oxidation of Zn films by irradiation with an excited metastable He beam

Abstract The oxidation of Zn films was attemmed by irradiation with an excited metastable atom beam of noble gas (He, Ne, Ar or Kr) in an oxygen atmosphere of the order of 10 −3 Pa. The excited metastable atoms were generated in a glass tube by an RF discharge and were ejected through a nozzle to a Zn film surface, to which a negative bias voltage was applied. The presence of the excited metastable atoms on the surface was confirmed by detection of the electron current ejected from a Cu plate which was irradiated with the excited metastable atom beam. For Ar and Kr, Zn films were hardly oxidized. On the other hand, transparent ZnO films were obtained for He and Ne. Judging from the fact that the energies of the excited metastable states of He and Ne are higher than the ionization potential of O 2 molecules, the oxidation of Zn films is attributed to the generation of O 2 + molecular ions on the film surface through the Penning ionization process by the excited metastable atom beam.

Preparation of Fe-N Films by Sputtering with He Gas

Fe-N films were deposited on glass substrates by rf sputtering with a mixture of Ar, He and N2 gases. The relationship between the properties of the films and the plasma species was investigated by optical emission spectroscopy analysis. In the Ar+He+N2 plasma, many N2+ molecular ions were generated by He atoms in neutral excited metastable states through the Penning ionization, and contributed to the reaction of Fe with nitrogen. Fe-N films prepared with a very low N2 content of less than 0.03% exhibited a larger magnetization than ¿-Fe.