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Ferromagnetic insulators are required for many new magnetic devices, such as dissipationless quantum-spintronic devices, magnetic tunneling junctions, etc. Ferromagnetic insulators with a high Curie temperature and a high-symmetry structure are critical integration with common single-crystalline oxide films or substrates. So far, the commonly used ferromagnetic insulators mostly possess low-symmetry structures associated with a poor growth quality and widespread properties. The few known high-symmetry materials either have extremely low Curie temperatures (≤16 K), or require chemical doping of an otherwise antiferromagnetic matrix. Here we present compelling evidence that the LaCoO3 single-crystalline thin film under tensile strain is a rare undoped perovskite ferromagnetic insulator with a remarkably high TC of up to 90 K. Both experiments and first-principles calculations demonstrate tensile-strain-induced ferromagnetism which does not exist in bulk LaCoO3 The ferromagnetism is strongest within a nearly stoichiometric structure, disappearing when the Co2+ defect concentration reaches about 10%. Significant impact of the research includes demonstration of a strain-induced high-temperature ferromagnetic insulator, successful elevation of the transition over the liquid-nitrogen temperature, and high potential for integration into large-area device fabrication processes.

A study analyzed molecular beam epitaxy grown InAs/GaSb superlattices, containing InSb-like interfacial layers by a combination of x-ray diffraction and structural refinement. The combined SUPREX//XRD experiments reveal that the absence of certain odd order satellite features in the x-ray data is due to asymmetric and inhomogeneous lattice strain.

Magneto-transport measurements have been made on strain-free In0.25Ga0.75Sb/InAs superlattices grown on GaSb substrates. The superior structural quality of these superlattices compared to older materials in the literature resulted in a much higher resolution of the Shubnikov-de Haas oscillations. Three separate conduction channels were observed. Measurements with the magnetic field in the plane of the sample indicated that the channel with the longer period was due to three dimensional-like conduction within the superlattice while the other two channels showed two dimensional behavior most likely associated with conduction at the surface or interfaces between the superlattice and bulk-like layers. Comparison with multi-carrier analysis indicated that the channel with intermediate period was due to hole conduction while the others were due to electron conduction. Oscillations were observed at temperatures up to 20?K. The concentration of the superlattice channel at low temperature was 5.93?×?1015 cm-3 while those of the two dimensional hole and electron channels were 1.64?×?1011 cm-2 and 5.20?×?1011 cm-2. [ABSTRACT FROM AUTHOR]

The electrical properties of In0.25Ga0.75Sb/InAs superlattices designed for use as very long wavelength infrared detectors were studied with magnetic field dependent transport measurements and multicarrier analysis. Two electron channels and one hole channel were identified. The low concentration, high mobility electron channel was identified with conduction within the superlattice. Residual electron concentrations in the superlattice are found to be in the high 1010 cm-2 range with mobilities on the order of 40 000 cm²/V s. The other electron and hole channels have significantly lower mobilities with concentrations in the 1011 cm-2 range and can have a significant impact on the resistivity, carrier concentration, and mobility as measured at a single magnetic field value in conventional transport measurements. [ABSTRACT FROM AUTHOR]

The first long-wave quantum-well infrared photodetectors that features lattice-matched n-doped InGaAlAs-InP materials system has been designed. Samples containing AlAs mole fractions of 0.0, 0.1 and 0.15 leads to cutoff wavelengths of 8.5, 13.3 and 19.4 micrometers, respectively. The measured intersubband photoresponse wavelength suggests the existence of a null conduction band offset for the In0.52Ga0.21Al0.27As-InP heterojunctions.

High-quality single-crystalline Bi6FeCoTi3O18 and LaBi5FeCoTi3O18 thin films were prepared by pulsed laser deposition. X-ray diffraction characterizations indicate a more disordered lattice structure of the LaBi5FeCoTi3O18 film. The magnetic measurement results demonstrated significantly enhanced ferromagnetism in the LaBi5FeCoTi3O18 film. The modulation of oxidation and hybridization states caused by substituting Bi with La was studied using the soft X-ray absorption spectroscopy. The spectroscopic results revealed the reduced concentration of oxygen vacancies and the more distorted lattice structure in the LaBi5FeCoTi3O18 film, which explained the enhanced ferromagnetism. [ABSTRACT FROM AUTHOR]

The temperature-dependent Hall effect and the Fourier transform photoconductivity (FTPC) were used to study deep levels between .1 and 1 electron volts in semi-insulating and high resistivity undoped horizontal Bridgman gallium arsenide. FTPC was effective in studying deep levels, identifying photoionization thresholds at .44, .8 and 1 electron volts and new thresholds near .25 electron volts and at .56 electron volts. New features were also observed in the .44 electron volt band, indicating that the defect for this level has a small lattice relaxation and Frank-Condon shift.

We report results of a systematic study of the structural and photoresponse properties of GaAs/{InAs quantum dot (QD)/InGaAs quantum well/GaAs} ×m multiple quantum dot (MQD) structures with m from 1 to 20 placed in n-GaAs/i(MQD)/n-GaAs configuration to act as quantum dot infrared photodetectors (QDIPs). Extremely low dislocation densities inferred from cross-sectional and plan-view transmission electron microscopy and the observed linear increase in photoluminescence intensity with MQD thickness reveal the high quality of these QDIP structures. Temperature and bias dependent dark and photocurrent measurements reveal dark current activation energies (Ea) increasing with the number of QD layers in a manner that indicates that Ea represents the built-in potential in the MQD region. These studies indicate the need for more quantitative modeling to guide optimal doping strategies and profiles to realize high photocurrents while maintaining acceptable dark current. [ABSTRACT FROM AUTHOR]

Würtzite semiconductors exhibit strong carrier-phonon coupling as well as strong Restrahlen-related absorption of radiation due to the interaction with optical phonons. For the GaN and AlN würtzites studied here, the optical phonon frequencies fall in the infrared region. With the transverse-optical phonon frequency ωt, and longitudinal-optical phonon frequency ωl, when light with frequencies ωt<ω<ωl is incident on a GaN or AlN film, the resonance with optical phonons will lead to strong absorption. In this paper, these effects are modeled and studied experimentally. Our studies show that the absorption is so strong that it is still significant even when the sample thickness is reduced to the submicron level. It is also found experimentally and theoretically that, not only the first harmonic, but also the second harmonic of the phonon frequency leads to strong absorption. Theoretical comparisons with experimental data and predicted transmission versus the energy of the incident light for different film thicknesses are presented. [ABSTRACT FROM AUTHOR]

The new advance in the area of II InAs/GaSb superlattices that have cutoff wavelength of ~3.7mum, is reported. The characteristic temperatures and the PL energy width were compared with those that have been reported for a similar cutoff wavelength in the material system.