The kinetics of diffusion processes occurring during the formation of polycrystalline Si1 -xGex nanostructures (x = 0.20, 0.35) by spark plasma sintering in the temperature range 20-1200 degrees C was studied for the first time. A mechanism for the formation of a SiGe solid solution is proposed as a result of a comprehensive study of the microstructure and phase composition of samples with particle sizes from 150 nm to 100 mu m, together with the analysis of experimental sintering maps. It is based on the phenomenon of mutual diffusion of Si and Ge atoms that occurs during the entire sintering process. For the selected sintering modes, the grain size of the formed SiGe corresponds to the size of the initial powder particles.

The kinetics of diffusion processes occurring during the formation of polycrystalline Si1 – xGex nanostructures (x = 0.20, 0.35) by spark plasma sintering in the temperature range 20–1200°C was studied for the first time. A mechanism for the formation of a SiGe solid solution is proposed as a result of a comprehensive study of the microstructure and phase composition of samples with particle sizes from 150 nm to 100 µm, together with the analysis of experimental sintering maps. It is based on the phenomenon of mutual diffusion of Si and Ge atoms that occurs during the entire sintering process. For the selected sintering modes, the grain size of the formed SiGe corresponds to the size of the initial powder particles.

The kinetics of diffusion processes occurring during the formation of polycrystalline Si 1-x Ge x nanostructures (x=0.20, 0.35) by spark plasma sintering in the temperature range 20-1200 o C was studied for the first time. A mechanism for the formation of a SiGe solid solution is proposed as a result of a comprehensive study of the microstructure and phase composition of samples with particle sizes from 150 nm to 100 μm, together with the analysis of experimental sintering maps. It is based on the phenomenon of mutual diffusion of Si and Ge atoms that occurs during the entire sintering process. For the selected sintering modes, the grain size of the formed SiGe corresponds to the size of the initial powder particles. Keywords: spark plasma sintering, solid solution SiGe, thermoelectric characteristics, figure of merit ZT.

The kinetics of diffusion processes occurring d0uring the formation of polycrystalline Si1-xGex nanostructures (x=0.20, 0.35) by electro-pulse plasma sintering in the temperature range 20-1200°C was studied for the first time. A mechanism for the formation of a solid solution of SiGe is proposed as a result of a comprehensive study of the microstructure and phase composition of samples with particle sizes from 150 nm to 100 μm, together with the analysis of experimental sintering maps. It is based on the phenomenon of mutual diffusion of Si and Ge atoms that occurs during the entire sintering process. For the selected sintering modes, the grain size of the formed SiGe corresponds to the size of the initial powder particles.

Thermoelectric Si 0,65 Ge 0,35 Sb δ materials have been fabricated by spark plasma sintering of Ge-Si-Sb powder mixture. The electronic properties of Si 0,65 Ge 0,35 Sb δ were found to be dependent on the uniformity of mixing of the components, which in turn is determined by the maximum heating temperature during solid-state sintering. Provided the concentration of donor Sb impurity is optimized the thermoelectric figure of merit for the investigated structures can be as high as 0.628 at the temperature of 490 °С, the latter value is comparable with world-known analogues obtained for Si 1- x Ge x P δ .

The electroluminescence of Schottky diodes with a composite ferromagnetic contact Au/Co/Au and a near-surface InGaAs/GaAs quantum well (QW) have been studied in magnetic fields B = 0 - 10 T and low temperature T similar to 2 K. The emission band due to recombination of the electrically injected holes with a two-dimensional electron gas (2DEG) in the QW shows values of a circular polarization degree P-C significantly higher than that in the reference nonmagnetic Au/GaAs diode, thus evidencing efficient spin injection. The nonmonotonic behavior of P-C(B) at high B correlates with a filling of the Landau levels and is attributed to the nonlinear screening of a random potential by the 2DEG. The systematic decrease of P, with increasing of the QW distance d(C) from the contact allows to estimate the hole transport spin-scattering length l(S) similar to 90 nm at a doping level similar to 10(17) cm(-3). Different factors of hole spin depolarization are revealed and discussed. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The circularly polarized electroluminescence of quantum-confined InGaAs/GaAs heterostructures with a ferromagnetic Ni(Co)/GaAs Schottky contact has been investigated. It is shown that the high degree of circular polarization (to 42%) is due to the injection of spin-polarized holes from the ferromagnetic metal. The dependence of the spin injection efficiency on the type of the metal/GaAs interface and the quantum well depth has been analyzed. The spin coherence length of holes was found to be ≈80 nm at 1.5 K.

The resistivity (ρ) of low mobility dilute 2D electron gas in an n- InGaAs / GaAs double quantum well (DQW) exhibits the monotonic "insulating-like" temperature dependence (dρ/dT < 0) at T = 1.8–70 K in zero magnetic field. This temperature interval corresponds to a ballistic regime (k B T τ /ħ > 0.1–3.5) for our samples, and the electron density is on an "insulating" side of the so-called B = 0 2D metal–insulator transition. We show that the observed features of localization and Landau quantization in a vicinity of the low magnetic-field-induced insulator–quantum Hall liquid transition is due to the σ xy (T) anomalous T-dependence.

Precision scanning of the (B⊥,B‖) plane between projections of the magnetic field perpendicular and parallel to the layers of an n-InxGa1−xAs∕GaAs (x≈0.2) double quantum well in measurements of its longitudinal magnetoresistance can reveal a number of features due to the complex energy spectrum of the double quantum well against the background of structure due to magnetic breakdown. Trajectories describing the features of the magnetoresistance on the (B⊥,B‖) plane can be described semiquantitatively on the basis of quasiclassical calculations of the quantization of the energy spectrum of the double quantum well under the influence of the perpendicular component of the field. Peaks due to magnetic breakdown are enhanced as the total value of the magnetic field increases. Their observed spin splitting corresponds to an effective value of the Landé factor ∣g*∣≈3.

We demonstrate efficient hole spin injection from a ferromagnetic metal (Ni) contact in a forward biased light emitting Schottky diode (LESD) fabricated on a GaAs based heterostructure with a quantum well (QW). The spin polarization of injected holes was detected by measuring circular polarization of the electroluminescence (EL) from the near surface InGaAs/GaAs QW. An intermediate gold layer has been used in order to improve the spin injection efficiency. Over 40% degree of circular polarization of the EL has been observed at T 2 K for the LESD structure with Au-Ni-Au Schottky contact.

In an n-InxGa1−xAs∕GaAs double quantum well (x≈0.2) the temperature dependence of the longitudinal resistance ρxx(T) of a 2D electron gas with low mobility and with an electron density close to the B=0 metal–insulator transition is of an “insulator” character in the temperature interval T=1.8–70K(kBTτ∕ℏ=0.1–3.8). Anomalous temperature dependence of σxy(B,T) in the region ωcτ=1 leads to a number of features of the transition from the regime of weak localization and electron–electron interaction to the quantum Hall effect regime at low magnetic fields.

A method of formation of two-dimensional structures containing a delta < Mn >-doped layer in GaAs and an InxGa1-x. As quantum well (QW) separated by a GaAs spacer ofthickness d = 4-6 nm is developed using laser evaporation of a metallic target during MOS hydride epitaxy. It is shown that, up to room temperature, these structures have ferromagnetic properties most likely caused by MnAs clusters. At low temperatures (T 30 K), the anomalous Hall elect is revealed to occur. This effect is related to hole scattering by Mn ions in GaAs and to the magnetic exchange between these ions and QW holes, which determines the spin polarization of the holes. The behavior of the negative magnetoresistance of these structures at low temperatures indicates the key role of quantum interference effects.

Precise scanning of the (B perpendicular to B parallel to) plane while measuring magnetoresistance of the n-InGaAs/GaAs double quantum well (DQW) reveals a number of peculiarities connected with intricate DQW energy spectrum, which are analyzed on the basis of quasiclassical calculations. Magnetic breakdown effects are also considered. Peaks due to the latter mechanism reveal spin-splittings (in spite of lower mobilities as compared with the traditional n-GaAs/AlGaAs DQWs) corresponding to an enhanced effective Lande g-factor.

A method of formation of two-dimensional structures containing a δ〈Mn〉-doped layer in GaAs and an InxGa1−x As quantum well (QW) separated by a GaAs spacer of thickness d = 4–6 nm is developed using laser evaporation of a metallic target during MOS hydride epitaxy. It is shown that, up to room temperature, these structures have ferromagnetic properties most likely caused by MnAs clusters. At low temperatures (T m ∼ 30 K), the anomalous Hall effect is revealed to occur. This effect is related to hole scattering by Mn ions in GaAs and to the magnetic exchange between these ions and QW holes, which determines the spin polarization of the holes. The behavior of the negative magnetoresistance of these structures at low temperatures indicates the key role of quantum interference effects.

Structurally perfect, high-purity silicon epilayers up to 20 μm in thickness, with a carrier concentration n = 1012 cm−3 are grown through thermal decomposition of silane. Experimental evidence is presented that the concentration of “electrically active” impurities in high-purity silane can be evaluated from the electrical parameters of Si epilayers grown from it.

The authors demonstrate efficient hole spin injection from a ferromagnetic metal (Ni) contact in a forward biased light emitting Schottky diode (LESD) fabricated on a GaAs based heterostructure with a quantum well (QW). The spin polarization of the injected holes was detected by measuring the circular polarization of the electroluminescence (EL) from the near surface InGaAs∕GaAs QW. An intermediate gold layer has been used in order to improve the spin injection efficiency. Over 40% degree of circular polarization of the EL has been observed at T=2K for the LESD structure with Au–Ni–Au Schottky contact.

Electroluminescence (EL) of InGaAs/GaAs heterostructures with quantum wells and ferromagnetic metal (Co, Ni)/GaAs Schottky contacts has been studied in magnetic fields up to 10 T at a temperature of 1.5 K. The EL line corresponding to the recombination of electrons with injected holes exhibits splitting into components corresponding to the Landau levels in the applied magnetic field and shows circular polarization that significantly exceeds the level typical of such structures with nonmagnetic (Au/GaAs) contacts. The degree of circular polarization ( P EL ) exhibits a nonmonotonic dependence on the applied magnetic field and is correlated with the filling of Landau levels. The maximum degree of circular polarization reached in the heterostructures studied is P EL = 40%.

The spectra of lateral photoconductivity in selectively doped SiGe/Si: B heterostructures with a two-dimensional hole gas are analyzed. It is revealed that the lateral photoconductivity spectra of these heterostructures exhibit two signals opposite in sign. The positive signal of the photoconductivity is associated with the impurity photoconductivity in silicon layers of the heterostructures. The negative signal of the photoconductivity is assigned to the transitions of holes from the SiGe quantum well to long-lived states in silicon barriers. The position of the negative photoconductivity signal depends on the composition of the quantum well, and the energy of the low-frequency edge of this signal is in close agreement with the calculated band offset between the quantum-confinement level of holes in the quantum well and the valence band edge in the barrier.