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We present the transfer of the spatially variant polarization of topologically structured light to the spatial spin texture in a semiconductor quantum well. The electron spin texture, which is a circular pattern with repeating spin-up and spin-down states whose repetition rate is determined by the topological charge, is directly excited by a vector vortex beam with a spatial helicity structure. The generated spin texture efficiently evolves into a helical spin wave pattern owing to the spin-orbit effective magnetic fields in the persistent spin helix state by controlling the spatial wave number of the excited spin mode. By tuning the repetition length and azimuthal angle, we simultaneously generate helical spin waves with opposite phases by a single beam., 6 pages, 4 figures

Long-range spin transport at room temperature is one of the indispensable technologies for realizing spintronics devices. In this study, we have investigated electron spin relaxation time of (110)-oriented GaAs superlattice having tunnel-coupled quantum wells for both lateral and vertical spin transport. It was revealed that the spin relaxation time at room temperature was 0.7 ns, about 7 times longer than that of bulk GaAs which has been used for conventional spin transport layer of spin-controlled lasers. This finding provides a novel method of controlling the spin relaxation time at room temperature and indicates that the superlattice structures are promising for spin transport layers in semiconductor-based spintronics devices.

In current materials science and technologies, surface effects on carrier and spin dynamics in functional materials and devices are of great importance. In this paper, we present the surface-sensitive probing of electron spin dynamics, performed by optical-pump-probe scanning tunneling microscopy (OPP-STM). Time-resolved spin lifetime information on a manganese (Mn)-deposited GaAs(110) surface was successfully obtained for the first time. With increasing Mn density via in situ evaporation, a nonlinear change in the spin lifetime in the picosecond range was clearly observed, while directly confirming the Mn density by STM. In comparison with the results obtained by the conventional OPP method, we have also demonstrated that the observed nonlinear spin lifetime behavior was surface-mediated, which can be characterized using only the surface-sensitive OPP-STM technique.

(110)-oriented GaAs-based quantum wells (QWs) are promising active layers of spin lasers because of long spin relaxation time at room temperature. So far, (110)GaAs/AlGaAs QWs have been investigated intensively and long carrier lifetime of several ns has been reported. In contrast, there have been few reports on the crystal growth of (110)InGaAs/(Al)GaAs QWs despite its great potential to the active layer, resulting in rather poor crystal quality with short carrier lifetime. In this study, we tried to grow high-quality (110)InGaAs/(Al)GaAs QWs by optimizing MBE growth conditions and obtained long carrier and spin lifetime (>1 ns) in the QWs grown with relatively high temperature and As/Ga flux ratio. This reveals that the (110)InGaAs/(Al)GaAs QWs are applicable to the active layer of spin lasers. In addition, we propose a novel structure for a spin transport layer between the ferromagnetic electrode (spin injector) and the active layer of spin laser.

We investigated the spin-orbit (SO) effective magnetic-field-induced spin precession of a high-mobility two-dimensional electron gas (2DEG) in a modulation-doped (001) GaAs/AlGaAs quantum well close to the persistent spin helix (PSH) state. The oscillating spin signal induced by the SO fields in zero external magnetic fields was clearly observed. When the photoexcited carrier density is sufficiently small compared with the 2DEG density, the spin precession length in the space domain was obtained by analyzing the precession frequency in the PSH regime. The excitation density dependence of the spin dynamics was reproduced well using the scattering time-dependent spin dynamics simulation. We revealed that the increase in the photoexcited carriers results in a transition from ballistic motion to diffusive motion, leading to a decrease in the spin-diffusion coefficient.

One of the important issues during the response to a mass disaster is the identification of victims. In this study, we verified the use of the occlusal morphology of molars for individual identification. The aim of this study was to establish a simple new method for identifying individuals from molar data. Using Python, we developed programming that included the perceptual Hash (pHash) function and the Hamming distance (HD) between antemortem data (AMD) and postmortem data (PMD). The AMD comprised 2,215 dental models. The PMD were selected from the AMD set and comprised 17 models from the same individual with changes over time. As a result, 16 PMD models (over 90%) were ranked in the top 5%. Although identification using only a single molar is difficult, there is the possibility of narrowing down victims' identity with high accuracy through verification using multiple teeth. This system is expected to be useful as a very simple method of identification.

We have systematically investigated the structural properties, carrier lifetimes, namely, photoluminescence (PL) lifetimes (τPL), and electron spin relaxation times (τs) in (110) GaAs/AlGaAs multiple quantum wells (MQWs) by using time-resolved PL measurements. The MQWs were grown by molecular beam epitaxy within a wide range of the growth temperature Tg (430–600 °C) and a high V/III flux ratio using As2. At 530 °C &lt, Tg &lt, 580 °C, we found that the quality of the heterointerfaces is significantly improved, resulting in τPL~40 ns at RT, one order of magnitude longer than those reported so far. Long τs (~6 ns) is also observed at RT.

Spin–orbit (SO) magnetic fields caused by the Dresselhaus SO interaction in slightly misoriented (110) InGaAs/InAlAs quantum wells (QWs) are investigated using the time-resolved and spatially resolved optical Kerr rotation technique. The Dresselhaus SO magnetic field is directed along the in-plane in the (001) QWs and along the out-of-plane in the (110) QWs. On the contrary, in QWs grown on a slightly misoriented (110) substrate, the out-of-plane and in-plane components of the Dresselhaus SO magnetic field coexist. In this study, the strong out-of-plane and the in-plane SO magnetic fields peculiar to the misoriented (110) InGaAs QWs are revealed at room temperature by analyzing spatially resolved diffusion-driven spin precession dynamics with a diagonally applied external magnetic field. Based on the scan position dependence of the spin precession frequency induced by the SO magnetic field, the simultaneous observations of the out-of-plane and the in-plane SO magnetic fields are achieved and Dresselhaus SO parameter is extracted to be 1.9 × 10 − 12 eV m. This value accounts for the scan position dependencies with various magnetic fields and reveals the reliability of the extracted SO parameter.

We investigate Rashba and Dresselhaus spin-orbit coefficients in (110)-grown GaAs/AlGaAs two-dimensional electron gas (2DEG) by employing time-resolved Kerr rotation microscopy. In III-V semiconductor 2DEG grown on (110) crystal orientation, while Dresselhaus spin-orbit field is perpendicular to the 2DEG plane, which maintains spin polarization, Rashba spin-orbit field randomizes spin polarization due to D'yakonov-Perel' spin relaxation mechanism. Therefore, it is important to evaluate both spin-orbit fields quantitatively. Here, we propose and examine the method for simultaneous extraction of Rashba and Dresselhaus fields in GaA/AlGaAs (110) 2DEG by employing spin diffusion.

We use Focused Electron Beam Deposition (FEBID) to directly write Cobalt magnetic nanoelements onto a micro-Hall magnetometer, which allows for high-sensitivity measurements of the magnetic stray field emanating from the samples. In a previous study [M. Pohlit et al., J. Appl. Phys. 117 (2015) 17C746] [ 21] we investigated thermal dynamics of an individual building block (nanocluster) of artificial square spin ice. In this work, we compare the results of this structure with interacting elements to the switching of a single nanoisland. By analyzing the survival function of the repeatedly prepared state in a given temperature range, we find thermally activated switching dynamics. A detailed analysis of the hysteresis loop reveals a metastable microstate preceding the overall magnetization reversal of the single nanoelement, also found in micromagnetic simulations. Such internal degrees of freedom may need to be considered, when analyzing the thermal dynamics of larger spin ice configurations on different lattice types.

We have investigated the electron spin relaxation time of a (110)-oriented GaAs/AlGaAs superlattice (SL) with tunnel-coupled quantum wells at room temperature. As the tunnel coupling between quantum wells increased, the spin relaxation time decreased. Even when the strength of tunnel coupling was as large as 25 meV, the spin relaxation time was 0.7 ns, about seven times longer than that of bulk GaAs which has been used as a conventional spin transport layer. This finding indicates that (110)-oriented SL structures are one of the potential candidates for spin transport in both in-plane and out-of-plane directions in semiconductor-based spintronic devices.

We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurements and micromagnetic simulations of dipolar coupled nanomagnets of Ni80Fe20 arranged in a double square ring-like geometry. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures, their reversal processes may undergo complex behavior. The details of such reversal behavior are observed as specific features in micro-Hall magnetometry data, which are comparable with the micromagnetic simulation data.We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurements and micromagnetic simulations of dipolar coupled nanomagnets of Ni80Fe20 arranged in a double square ring-like geometry. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures, their reversal processes may undergo complex behavior. The details of such reversal behavior are observed as specific features in micro-Hall magnetometry data, which are comparable with the micromagnetic simulation data.

We combined scanning tunneling microscopy and locally resolved magnetic stray field measurements on the ferromagnetic semimetal EuB_{6}, which exhibits a complex ferromagnetic order and a colossal magnetoresistance effect. In a zero magnetic field, scanning tunneling spectroscopy visualizes the existence of local inhomogeneities in the electronic density of states, which we interpret as the localization of charge carriers due to the formation of magnetic polarons. Micro-Hall magnetometry measurements of the total stray field emanating from the end of a rectangular-shaped platelike sample reveals evidence for magnetic clusters also in finite magnetic fields. In contrast, the signal detected below the faces of the magnetized sample measures a local stray field indicating the formation of pronounced magnetic inhomogeneities consistent with large clusters of percolated magnetic polarons.

Dislocations were introduced in wurtzite zinc oxide single crystals by Vickers indentations on { 2 1 ¯ 1 ¯ 0 } and { 10 1 ¯ 0 } surfaces at elevated temperatures, and their slip systems were determined by transmission electron microscopy combined with etch pit observations. The observed system for { 2 1 ¯ 1 ¯ 0 } indentations was { 10 1 ¯ 1 ¯ } 〈 1 ¯ 2 1 ¯ 0 〉 or (0001) 〈 1 ¯ 2 1 ¯ 0 〉 , while that for { 10 1 ¯ 0 } indentations was { 10 1 ¯ 0 } 〈 1 ¯ 2 1 ¯ 0 〉 . Activation of the slip systems was briefly discussed in terms of the Peierls stress and resolved shear stress acting on the slip systems.

In 〈 0 4 ¯ 41 〉 - oriented lithium niobate single crystals, striae of planar defect lying on nearly ( 2 ¯ 110 ) were formed during the Czochralski growth. A stria was a small angle tilt boundary including a set of undissociated edge dislocations with the Burgers vector of a /3[ 2 ¯ 110 ], arranged at similar intervals of about 1 μ m . The dislocations extended perpendicular to the growth interface, leaving from the basal plane, presumably for the reduction of their strain energy during the growth. The formation process was discussed in terms of thermal stress at the growth interface during crystallization.

We discuss the effect of the atomic interfacial structure on the Schottky barrier height in Fe/GaAs films. HRTEM image simulations, produced using the microscopy software JEMS, were used to predict the interfacial structure of Fe/GaAs thin films. Comparisons between experimental images, obtained using a JEOL FS2200 microscope, and the image simulations show the interfaces to contain various structures. This leads to regions with different barrier properties giving a distribution of barrier heights. This would create preferential regions for tunnelling across the film which would dominate device characteristics.

The authors studied a GaAs/Al0.3Ga0.7As hetero-nanostructure etching process, neutral beam (NB) etching with chlorine (Cl2) and argon (Ar) mix gas. The effect of different mixing ratios of chlorine and argon has been investigated. The results showed that when pure chlorine NB (Cl-NB) was used, the pillar formation problem was observed on the etched surface. By increasing the Ar/(Cl2+Ar) gas mixing ratio, the pillar can be eliminated and the roughness of etched surface smoothed. As an Ar/(Cl2+Ar) gas mixing ratio of 78% was used, the root-mean-square roughness of etched surfaces of both GaAs and Al0.3Ga0.7As is about 0.6 nm, which is almost the same as those of as-received samples. Meanwhile, the etching selectivity of GaAs/Al0.3Ga0.7As can be kept close to 1, which would help to etch a clear and smooth profile. Additionally, the high-resolution transmission-electron microscopy image of the GaAs etch profile shows that no crystalline defect was observed on the etched surface.

The quantum Hall effect arises from the cyclotron motion of charge carriers in two-dimensional systems. However, the ground states related to the integer and fractional quantum Hall effect, respectively, are of entirely different origin. The former can be explained within a single-particle picture; the latter arises from electron correlation effects governed by Coulomb interaction. The prerequisite for the observation of these effects is extremely smooth interfaces of the thin film layers to which the charge carriers are confined. So far, experimental observations of such quantum transport phenomena have been limited to a few material systems based on silicon, III-V compounds and graphene. In ionic materials, the correlation between electrons is expected to be more pronounced than in the conventional heterostructures, owing to a large effective mass of charge carriers. Here we report the observation of the fractional quantum Hall effect in MgZnO/ZnO heterostructures grown by molecular-beam epitaxy, in which the electron mobility exceeds 180,000 cm(2) V(-1) s(-1). Fractional states such as ν = 4/3, 5/3 and 8/3 clearly emerge, and the appearance of the ν = 2/5 state is indicated. The present study represents a technological advance in oxide electronics that provides opportunities to explore strongly correlated phenomena in quantum transport of dilute carriers.

We implement time-resolved Kerr microscopy (TRKM) system with ∼ 1 μ m spatial resolution for observation of coupled electron–nuclear spin dynamics such as dynamic nuclear polarization (DNP) in a local area of the laser spot. From TRKM measurements, Larmor precession of electron spins injected by right ( σ + ) or left ( σ − ) circular polarized pump pulse is detected. The difference of the precession frequencies between σ + and σ − pumping corresponds to the polarization-dependent nuclear magnetic field caused by DNP. This indicates that we successfully detect coupled electron–nuclear spin dynamics in a local area of the laser spot size of ∼ 1.5 × 1.5 μ m 2 . Furthermore, we show the pump and probe power dependences of DNP in high optical intensity region. All-optical NMR is also demonstrated at arbitrary frequencies by controlling acousto-optical modulator.

In-plane magnetic anisotropy of 40-μm-long (Ga,Mn)As wires with different widths (0.4, 1.0, and 20 μm) has been investigated between 5 and 75 K by measuring anisotropic magneto-resistance (AMR). The wires show in-plane 〈1 0 0〉 cubic and [−1 1 0] uniaxial anisotropies, and an additional lithography-induced anisotropy along the wire direction in narrow wires with width of 0.4 and 1.0 μm. We derive the temperature dependence of the cubic, uniaxial, and lithography-induced anisotropy constants from the results of AMR, and find that a sizable anisotropy can be provided by lithographic means, which allows us to control and detect the magnetization reversal process by choosing the direction of the external magnetic fields.

We discuss the effect of annealing on the interfacial structure of Fe/GaAs films, with 2 × 4 surface reconstructions, and the subsequent effect on the Schottky barrier height. Images of the interfaces indicate that the annealing process can greatly reduce the level of atomic mixing. A study of the I-V characteristics of Fe/GaAs Schottky barrier diodes, in a wide temperature range of 10-300 K, reveals a strong temperature dependence for the unannealed case, arising from the presence of mixed surface states. The annealing process reduces the existence of the interfacial states, leading to more ideal behavior, with a reduced temperature dependence of the Schottky behavior.

Parallel twin boundaries arranged at similar intervals of nanometer length, that emitted an intense monochromatic light polarized parallel to the boundaries, were self-organized in an indirect-gap AlGaAs epilayer; the epilayer was grown on a rough As-deficient surface of an AlGaAs(0 0 1) substrate with any lattice constant, by conventional metal-organic chemical-vapor deposition. Most boundaries were of Σ3-type on {111}B, and they extended from the interface between the epilayer and the substrate. There existed no compositional fluctuation around the boundaries. The formation mechanism was discussed.

In this paper, recent developments in magnetic tunnel junctions (MTJs) are reported with their potential impacts on integrated circuits. MTJs consist of two metal ferromagnets separated by a thin insulator and exhibit two resistances, low (Rp) or high (Rap) depending on the relative direction of ferromagnet magnetizations, parallel (P) or antiparallel (AP), respectively. Tunnel magnetoresistance (TMR) ratios, defined as (Rap $Rp)/Rp as high as 361%, have been obtained in MTJs with Co40Fe40B20 fixed and free layers made by sputtering with an industry-standard exchange-bias structure and post deposition annealing at Ta = 400 degC. The corresponding output voltage swing DeltaV is over 500 mV, which is five times greater than that of the conventional amorphous Al-O-barrier MTJs. The highest TMR ratio obtained so far is 500% in a pseudospin-valve MTJ annealed at Ta = 475 degC, showing a high potential of the current material system. In addition to this high-output voltage swing, current-induced magnetization switching (CIMS) takes place at the critical current densities (JCO) on the order of 106 A/cm2 in these MgO-barrier MTJs. Furthermore, high antiferromagnetic coupling between the two CoFeB layers in a synthetic ferrimagnetic free layer has been shown to result in a high thermal-stability factor with a reduced JCO compared to single free-layer MTJs. The high TMR ratio enabled by the MgO-barrier MTJs, together with the demonstration of CIMS at a low JCO, allows development of not only scalable magnetoresistive random-access memory with feature sizes below 90 nm but also new memory-in-logic CMOS circuits that can overcome a number of bottlenecks in the current integrated-circuit architecture

We report on a comprehensive characterization of the fluctuation properties of micro-Hall magnetometers based on a two-dimensional electron system (2DES) in δ-doped GaAs/AlGaAs semiconductor heterostructures. The analysis of the temperature- and frequency-dependent noise in a simple model of non-exponential kinetics reveals a distribution of activation energies for the 1/f α-type fluctuations. In addition to the 1/f-noise, two-level fluctuators with distinct energies are observed. We identify deep donor levels in AlGaAs (DX centers) as the predominant source of 1/f-noise and discuss the effect of the corresponding energy signature of these defect levels on the device performance in different temperature regimes, where we find an extremely low noise level at temperatures below ∼ 100 K and above ∼ 200 K.

We have fabricated a three terminal device integrating a (Ga,Mn)As Esaki diode and a light emitting diode (LED) to investigate the bias-voltage dependence of the injection of spin polarized electrons. The electroluminescence polarization (PEL) from the LED was measured under Faraday configuration as a function of bias voltages applied independently to the Esaki diode and to the LED. The polarization shows strong dependence on the bias applied to the Esaki diode when the LED bias is fixed. The maximum PEL of 32.4% was observed when the valence electrons near the Fermi energy of (Ga,Mn)As are injected into the LED. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A novel ethyl methacrylate (EMA) resin was developed to overcome the tissue, organ and systemic damage associated with the residual monomer of conventional methyl methacrylate (MMA) resin bone cement. EMA resin is a chemical/ photopolymerizable material and is easy to handle during clinical procedures. The biocompatibility of EMA was evaluated in accordance with ISO10993-6. No inflammatory response was observed 1 and 9 weeks after implantation in the dorsal subcutaneous tissue of ddY mice. EMA resin also demonstrated better biocompatibility when compared with conventional bone cements. Poly-l-lactic acid (PLLA) was used as a carrier for bone morphogenetic protein (BMP) and added to the EMA slurry. The EMA-PLLA composite membrane was sticky and BMP readily adhered to its surface. The EMA-PLLA-BMP composite membrane induced new bone formation, the new bone growing in the shape of the EMA in the thigh muscle pouch of ddY mice. This novel EMA resin has many potential clinical applications.

We have previously synthesized a novel acrylic resin monomer, methacryloyloxyethyl methyl succinate (TA). The aim of this in vitro study, therefore, was to examine its influence on cell viability using L-929 mouse fibroblasts and then compare the results with MMA, EMA, and LMA. Medium containing each monomer was changed every 15 minutes as some monomers were volatile. After one hour of exposure, these mediums were replaced with a normal medium and cells were further incubated for 72 hours. IC50 value for each monomer was determined, and chronological cell viability and cytomorphologic observation were evaluated. Viability was impaired in a dose-dependent manner. All monomers, except TA, tended to correlate between molecular weight and cell viability. On the other hand, TA showed excellent viability and did not impair growth abruptly. These results thus demonstrated that cellular damage by TA was much lower than that by other monomers.

We present systematic studies of the excess low-frequency noise in GaAs/AlxGa1−xAs heterostructure 2DES Hall devices. We studied structures of various sizes made from different wafer materials. In larger samples a significant suppression of the 1/f noise level by gating has been observed. In structures as small as (0.45×0.45) μm2 the overall noise level is significantly higher and non-Gaussian-type noise dominates at all temperatures. Random telegraph fluctuations finally limit the device miniaturization in these materials.

Molecular beam epitaxy of GaSb films, with several percents of Cr, and their characterization are reported. Their electric and magnetic properties depend on their growth temperature and Cr composition. Although magnetization measurements reveal that all the films are ferromagnetic even at room temperature, this is most probably due to the precipitation of ferromagnetic zincblende CrSb. The magnetotransport measurements show that Cr spins may couple antiferromagnetically in GaSb host matrix.

Electron spin dynamics in strained In 0.1 Ga 0.9 As/Al 0.4 Ga 0.6 As quantum wells (QWs) on (1 0 0) and (1 1 0) -oriented substrates are investigated by time-resolved Faraday rotation. We find that the spin relaxation time in (1 1 0) QWs is 6 times longer than that in (1 0 0) QWs at low temperatures, which is strongly reduced by applying magnetic fields. The sign of g -factor is found positive and its magnitude decreases with increasing well width, in the well width range investigated here.

We demonstrate electrical electron spin injection in a p+-(Ga,Mn)As/n+-GaAs tunnel junction with an n-GaAs/(In,Ga)As/p-GaAs light emitting diode (LED). By applying a reverse bias to the p+-(Ga,Mn)As/n+-GaAs junction (forward bias to the LED), we observed clear hysteresis in electroluminescence (EL) polarization. The magnitude of the EL polarization, which does not depend critically on the spacer layer thickness up to 800 nm, is found to be about five times greater than that of the hole spin injection.

We have investigated the magnetotransport properties of field-effect transistors (FET) having a III-V ferromagnetic semiconductor channel layer. One can control not only the ferromagnetic transition temperature T C but also the magnetization and the coercive force of (In,Mn)As channel layers isothermally and reversibly by gate electric fields. A small change of the magnetization upon application of gate electric fields is also observed in FETs with a (Ga,Mn)As channel. Results on a (Al,Ga,Mn)As channel FET are also presented.

Ferromagnetic III–V semiconductors, such as (Ga,Mn)As and (In,Mn)As, are among the promising materials in the field of semiconductor spintronics because of their good compatibility with the high quality III–V heterostructures. We show several examples of the novel spin-related properties of heterostructures containing a ferromagnetic component: (1) all-semiconductor (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As trilayers exhibiting spin-dependent scattering and tunneling magnetoresistance; (2) resonant tunneling structures with (Ga,Mn)As emitter, where spontaneous spin-splitting of the valence band is probed; (3) spin-light emitting diodes, in which spin-injection can be observed and (4) field effect transistor structures with a (In,Mn)As channel layer, making it possible to control the ferromagnetism by an electric field.

Ferromagnetic (Ga,Mn)As epitaxial layers with zincblende structure have been grown on Si (1 0 0) substrates employing a three-step method using molecular beam epitaxy. Magnetic measurements reveal that the ferromagnetic transition temperature is 48 K for a layer with a lattice constant of 0.567 nm, which corresponds to a nominal Mn composition of 2%. When grown directly on Si without the three-step method, the same set of growth parameters results in a (Ga,Mn)As layer with a ferromagnetic order below 25 K. The difference of magnetic property between these two samples is attributed to the quality of the (Ga,Mn)As layer which originates from the different growth methods.

Transport properties of (Ga,Mn)As/GaAs/p-GaAs p–i–p diodes were studied to manifest the potential barrier in the valence band at (Ga,Mn)As/GaAs junctions. The temperature dependences of the current–voltage characteristics exhibit typical thermionic emission behaviors, which gives the effective potential barrier height of 87– 140 meV for holes injected from (Ga,Mn)As to undoped GaAs.

Electric-field control of carrier-induced ferromagnetism is demonstrated for field-effect transistor structure of magnetic semiconductor (In,Mn)As. By varying the gate electric field one can control the ferromagnetic transition temperature isothermally and reversibly.

III–V ferromagnetic semiconductors allow epitaxial integration of ferromagnetism with nonmagnetic semiconductor heterostructures and offer opportunities to explore properties that combine conventional semiconductor physics with magnetic cooperative phenomena. Here, we review spin-dependent phenomena observed in III–V-based ferromagnetic semiconductor heterostructures, which include spin-dependent scattering, tunnel magnetoresistance, resonant tunneling with ferromagnetic emitter, spin injection, and electric field control of ferromagnetism.

We review recent studies on spin-dependent properties of structures made of ferromagnetic GaAs, (Ga,Mn)As, aimed to lay the ground for semiconductor spin-electronics (spintronics). Introduction of magnetic ion, Mn, in GaAs leads to hole-induced ferromagnetism, the origin of which is explained in terms of a mean-field theory. Due to exchange interaction between spins of carriers and localized magnetic electrons, spin-splitting of the semiconductor bands takes place when ferromagnetism sets in, and carriers become spin polarized. This spontaneous spin polarization leads to spin-dependent scattering and tunnel magnetoresistance in semiconducting structures. Electrical spin injection across a ferromagnetic/nonmagnetic semiconductor heterojunction and into an InGaAs quantum well is also demonstrated using the spin polarized carriers in ferromagnetic (Ga,Mn)As.

We present experimental results on quantum-well photodetectors for visible or near-infrared and middle- or far-infrared dual-band detection. We report on two types of devices based on (1) InGaAs/InP and (2) GaAs/AlGaAs quantum wells. In the first case, InGaAs/InP quantum-well infrared photodetectors (QWIPs) for both near and middle infrared spectra are shown. In the second case, large bandgap top contacts were used on standard GaAs/AlGaAs QWIPs so that visible light could reach the quantum-well region and be absorbed via interband transitions. Two large band gap top contacts were investigated, using a high Al fraction AlGaAs and a short period GaAs/AlAs superlattice. We evaluate and analyze the detector performance. We find that such devices are potentially useful for applications involving dual-band simultaneous detection and imaging.

Magneto-electroluminescence properties of ferromagnetic/nonmagnetic semiconductor pn junction light emitting diodes (LEDs) are presented. A ferromagnetic p-type (Ga,Mn)As layer is grown on i-(In,Ga)As quantum well (QW)/n-GaAs so that the degree of spin polarization of holes injected from (Ga,Mn)As into GaAs can be probed by analyzing the polarization of light emitted from the LED structures. The EL polarization as a function of magnetic field exhibits clear hysteresis below the ferromagnetic transition temperature of (Ga,Mn)As, which is the evidence that spin-polarized electrical current is injected into nonmagnetic semiconductor.