Search

Spin gapless semiconductors have been regarded as the most promising candidates for spin injection materials due to the complete (100%) spin polarization and the conductivity between half-metals and semiconductors. To explore the potential spintronic applications of the quaternary Heusler alloy CoFeMnSi (CFMS), a recently fabricated spin gapless semiconductor with a high Curie temperature of 620 K, we design the GaAs/CFMS heterostructure and the CFMS/GaAs/ CFMS magnetic tunnel junction (MTJ). It is found from the first-principles calculations combined with nonequilibrium Green’s function that the heterostructure exhibits an excellent spin filtering effect and spin diode effect and the MTJ has a large tunnel magnetoresistance ratio (up to 2 x 103), which are explained from the calculated spin-dependent band structure and transmission spectrum. These perfect spin transport characteristics make CFMS a promising candidate for spintronic applications. [ABSTRACT FROM AUTHOR]

We present ab-initio calculations of the phonon thermal transport properties of topological insulator TlBiSe2. Our results point to a very low lattice thermal conductivity, comparable or lower than those of some popular good thermoelectric materials. Furthermore, we find a slight thermal anisotropy between the in-plane and cross-plane directions in TlBiSe2, markedly smaller than those of van-der-Waals topological insulators explored so far. These conclusions are confirmed and explained by comprehensive analysis of the phonon spectrum of TlBiSe2. The combination of ultra-low lattice thermal conductivity and small anisotropy makes TlBiSe2 a promising candidate for thermoelectric applications. [ABSTRACT FROM AUTHOR]

BiFeO3 thin films were epitaxially grown on (001) GaAs substrate by pulsed laser deposition with Nb doped SrTiO3 as a buffer layer. Piezoresponse force microscopy images exhibit effective ferroelectric switching of the heterostructure. The temperature-dependent current-voltage characteristics of the heterostructure reveal a resistance switching phenomenon and diode-like behavior with a rectifying ratio of 2 x 10² at the applied voltage of ±13.4V. The electrical transport mechanism in the heterostructure has been illustrated by constructing the energy band structure. In addition, the resistance switching behavior in the heterostructure could be explained by the polarization modulation of the depletion region at the interface of the semiconductor and the ferroelectric layers. [ABSTRACT FROM AUTHOR]

We grow epitaxial (La0.8Pr0.2)0.67Ca0.33MnO3 films simultaneously on the lattice-closely-matched substrates, cubic (LaAlO3)0.3(Sr2AlTaO6)0.7 [LSAT(001)] and orthorhombic NdGaO3 [NGO(001) and NGO(110)]. While all as-grown films show a ferromagnetic-metallic (FM) ground state as observed for the bulk target, the annealed films show quite different magnetotransport behavior as follows: on NGO(110) they show a robust FM ground state, on LSAT(001) and NGO(001) however, they show surprisingly a coexisted antiferromagnetic insulating state with high phase instability in a wide temperature range. The phase coexistence being easily induced via the control of anisotropic epitaxial strain suggests that the phase separation in manganites could be elastically driven, and thus can be strain-engineered for devices applications. [ABSTRACT FROM AUTHOR]

The domain structure in epitaxial La0.7Sr0.3MnO3 films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7(001) substrates has been investigated by x-ray reciprocal space maps on (003), (103), (103), (013), and (013) reflections in the high-resolution scattering zone containing the c* axis, and the transmission electron microscopy. We revealed that at above 20 nm, the films show clearly a low symmetry monoclinic phase, and the shear strain relaxation can induce a patterned domain structure and in-plane superlattice in the films. The domain width versus the film thickness and the shear strain effect on the Curie temperature of the films were also discussed. [ABSTRACT FROM AUTHOR]

The base-collector junction of GaAs/AlGaAs single heterojunction bipolar transistors has been observed to emit light at avalanche breakdown. The spectral distribution curve exhibits broad peaks at 2.03 and 1.43 eV, with the intensities dependent upon the reverse current. These observations suggest that electrons, excited to the upper conduction band by the field, lose their energy by impact ionizing electron-hole pairs and producing the 2.03 eV light, which corresponds to the threshold energy for electron impact ionization. The band-edge emission is the result of direct-gap free-carrier recombination and self-absorption of the high-energy transition. [ABSTRACT FROM AUTHOR]

Electrical properties of p+-Ge/N-AlGaAs (and N-GaAs) are studied as a function of temperature and current conduction mechanisms are outlined. Junctions with Ge grown on GaAs and AlGaAs show ideality factors of unity and 1.03 at room temperature, respectively. Temperature-dependent current-voltage (I-V) and room-temperature capacitance-voltage (C-V) characterization are employed to determine the built-in voltage (Vbi) of the two diode structures. For Ge/GaAs, a valence-band discontinuity of 0.49±0.05 eV is measured which is in good agreement with the value deduced from photoemission studies. Implications of p+-Ge base in AlGaAs/Ge/GaAs double-heterojunction bipolar transistors (DHBTs) are discussed. [ABSTRACT FROM AUTHOR]

We present ab-initio calculations of the phonon thermal transport properties of topological insulator TlBiSe2. Our results point to a very low lattice thermal conductivity, comparable or lower than those of some popular good thermoelectric materials. Furthermore, we find a slight thermal anisotropy between the in-plane and cross-plane directions in TlBiSe2, markedly smaller than those of van-der-Waals topological insulators explored so far. These conclusions are confirmed and explained by comprehensive analysis of the phonon spectrum of TlBiSe2. The combination of ultra-low lattice thermal conductivity and small anisotropy makes TlBiSe2 a promising candidate for thermoelectric applications. [ABSTRACT FROM AUTHOR]