arXiv subjects

Masaaki Tanaka

Publications and source records attributed to Masaaki Tanaka.

102 records · Page 6Linked to original sources

arXiv2010

Magnetoresistance of a spin MOSFET with ferromagnetic MnAs source and drain contacts

Spin-dependent transport was investigated in a spin metal-oxide-semiconductor field-effect transistors (spin MOSFET) with ferromagnetic MnAs source and drain (S/D) contacts. The spin MOSFET of bottom-gate type was fabricated by photolithography using an epitaxial MnAs film grown on a silicon-on-insulator (SOI) substrate. In-plane magnetoresistance showed spin-valve-type hysteretic behavior, when the measurements were performed with constant source-drain and source-gate biases. By comparing with the magnetization-related resistance change resulting from the MnAs contacts, we conclude that the spin-polarized electrons are injected from the MnAs source into the Si MOS inversion channel, and detected by the MnAs drain.

cond-mat.mtrl-sci↗

arXiv2009

Quantum-level control in a III-V-based ferromagnetic-semiconductor heterostructure with a GaMnAs quantum well and double barriers

We investigate the spin-dependent tunneling properties in a three-terminal III-V-based ferromagnetic-semiconductor heterostructure with a 2.5-nm-thick GaMnAs quantum well (QW) and double barriers. We successfully control the quantum levels and modulate the spin-dependent current with varying the voltage of the electrode connected to the GaMnAs QW. Our results will open up a new possibility for realizing three-terminal spin resonant-tunneling devices.

cond-mat.mtrl-sci↗

arXiv2009

GaMnAs-based magnetic tunnel junctions with an AlMnAs barrier

We investigate the spin-dependent transport of GaMnAs-based magnetic tunnel junctions (MTJs) containing a paramagnetic AlMnAs barrier with various thicknesses. The barrier height of AlMnAs with respect to the Fermi level of GaMnAs is estimated to be 110 meV. We observe tunneling magnetoresistance (TMR) ratios up to 175% (at 2.6 K), which is higher than those of the GaMnAs-based MTJs with other barrier materials in the same temperature region. These high TMR ratios can be mainly attributed to the relatively high crystal quality of AlMnAs and the suppression of the tunneling probability near at the in-plane wave-vector k||=0.

cond-mat.mtrl-sci↗

arXiv2009

A new spin-functional MOSFET based on magnetic tunnel junction technology: pseudo-spin-MOSFET

We fabricated and characterized a new spin-functional MOSFET referred to as a pseudo-spin-MOSFET (PS-MOSFET). The PS-MOSFET is a circuit using an ordinary MOSFET and magnetic tunnel junction (MTJ) for reproducing functions of spin-transistors. Device integration techniques for a bottom gate MOSFET using a silicon-on-insulator (SOI) substrate and for an MTJ with a full-Heusler alloy electrode and MgO tunnel barrier were developed. The fabricated PS-MOSFET exhibited high and low transconductance controlled by the magnetization configurations of the MTJ at room temperature. This is the first observation of spin-transistor operations for spin-functional MOSFETs.

cond-mat.mtrl-sci↗

arXiv2007

Spin valve effect by ballistic transport in ferromagnetic metal (MnAs) / semiconductor (GaAs) hybrid heterostructures

We demonstrate the spin valve effect by ballistic transport in fully epitaxial MnAs ferromagnetic metal / GaAs semiconductor / GaAs:MnAs granular hybrid heterostructures. The GaAs:MnAs material contains ferromagnetic MnAs nanoparticles in a GaAs matrix, and acts as a spin injector and a spin detector. Although the barrier height of the GaAs/MnAs interface was found to be very small, relatively large magnetoresistance was observed. This result shows that by using ballistic transport, we can realize a large spin valve effect without inserting a high tunnel barrier at the ferromagnetic metal / semiconductor interface.

cond-mat.mtrl-sci↗

arXiv2007

Reconfigurable Logic Gates Using Single-Electron Spin Transistors

We propose and numerically analyze novel reconfigurable logic gates using "single-electron spin transistors" (SESTs), which are single-electron transistors (SETs) with ferromagnetic electrodes and islands. The output characteristics of a SEST depend on the relative magnetization configuration of the ferromagnetic island with respect to the magnetization of the source and the drain, i.e., high current drive capability in parallel magnetization and low current drive capability in antiparallel magnetization. The summation of multiple input signals can be achieved by directly coupling multiple input gate electrodes to the SEST island, without using a floating gate. A Tucker-type inverter with a variable threshold voltage, a reconfigurable AND/OR logic gate, and a reconfigurable logic gate for all symmetric Boolean functions are proposed and simulated using the Monte Carlo method.

cond-mat.mtrl-sci↗

arXiv2007

Spin-dependent transport properties in GaMnAs-based spin hot-carrier transistors

We have investigated the spin-dependent transport properties of GaMnAs-based three-terminal semiconductor spin hot-carrier transistor (SSHCT) structures. The emitter-base bias voltage VEB dependence of the collector current IC, emitter current IE, and base current IB shows that the current transfer ratio alpha (= IC / IE) and the current gain beta (= IC / IB) are 0.8-0.95 and 1-10, respectively, which means that GaMnAs-based SSHCTs have current amplifiability. In addition, we observed an oscillatory behavior of the tunneling magnetoresistance (TMR) ratio with the increasing bias, which can be explained by the resonant tunneling effect in the GaMnAs quantum well.

cond-mat.mtrl-sci↗

arXiv2006

Magneto-optical and magnetotransport properties of heavily Mn-doped GaMnAs

We have studied the magneto-optical and magnetotrasnport properties of GaMnAs thin films with high Mn concentrations (x= 12.2 - 21.3%) grown by molecular-beam epitaxy. These heavily Mn-doped GaMnAs films were formed by decreasing the growth temperature to as low as 150-190 degree C and by reducing the film thickness to 10 nm in order to prevent precipitation of hexagonal MnAs clusters. Magnetic circular dichroism (MCD) and anomalous Hall effect measurements indicate that these GaMnAs films have the nature of intrinsic ferromagnetic semiconductors with high ferromagnetic transition temperature up to 170 K.

cond-mat.mtrl-sci↗

arXiv2005

Precipitation of amorphous ferromagnetic semiconductor phase in epitaxially grown Mn-doped Ge thin films

We investigated the origin of ferromagnetism in epitaxially grown Mn-doped Ge thin films. Using low-temperature molecular beam epitaxy, Mn-doped Ge films were successfully grown without precipitation of ferromagnetic Ge-Mn intermetallic compounds, such as Mn5Ge3. Magnetic circular dichroism measurements revealed that the epitaxially grown Mn-doped Ge films exhibited clear ferromagnetic behavior, but the Zeeman splitting observed at the critical points was not induced by the s,p-d exchange interactions. High-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy analyses show phase separation of amorphous Ge1-xMnx clusters with high Mn content from a Mn-free monocrystalline Ge matrix. Since amorphous Ge1-xMnx was characterized as a homogeneous ferromagnetic semiconductor, the precipitation of the amorphous Ge1-xMnx clusters is the origin of the ferromagnetic semiconductor behavior of the epitaxially grown Mn-doped Ge films.

cond-mat.mtrl-sci↗

arXiv2004

Novel Reconfigurable Logic Gates Using Spin Metal-Oxide-Semiconductor Field-Effect Transistors

We propose and numerically simulate novel reconfigurable logic gates employing spin metal-oxide-semiconductor field-effect transistors (spin MOSFETs). The output characteristics of the spin MOSFETs depend on the relative magnetization configuration of the ferromagnetic contacts for the source and drain, that is, high current-drive capability in the parallel magnetization and low current-drive capability in the antiparallel magnetization [S. Sugahara and M. Tanaka: Appl. Phys. Lett. 84 (2004) 2307]. A reconfigurable NAND/NOR logic gate can be realized by using a spin MOSFET as a driver or an active load of a complimentary MOS (CMOS) inverter with a neuron MOS input stage. Its logic function can be switched by changing the relative magnetization configuration of the ferromagnetic source and drain of the spin MOSFET. A reconfigurable logic gate for all symmetric Boolean functions can be configured using only five CMOS inverters including four spin MOSFETs. The operation of these reconfigurable logic gates was confirmed by numerical simulations using a simple device model for the spin MOSFETs

cond-mat.mtrl-sci↗

arXiv2003

Properties and Curie Temperature (130 K) of Heavily Mn-doped Quaternary Alloy Ferromagnetic Semiconductor (InGaMn)As Grown on InP

We have studied magnetic properties of heavily Mn-doped [(In0.44Ga0.56)0.79Mn0.21]As thin films grown by low-temperature molecular-beam epitaxy (LT-MBE) on InP substrates. The (InGaMn)As with high Mn content (21%) was obtained by decreasing the growth temperature to 190 degC. When the thickness of the [(In0.44Ga0.56)0.79Mn0.21]As layer is equal or thinner than 10 nm, the reflection high-energy electron diffraction (RHEED) pattern and transmission electron microscopy (TEM) show no MnAs clustering, indicating that a homogeneous single crystal with good quality was grown. In the magnetic circular dicroism (MCD) measurement, large MCD intensity and high Curie temperature of 130 K were observed.

cond-mat.mtrl-sci↗

arXiv2001

Growth and Properties of Quaternary Alloy Magnetic Semiconductor (InGaMn)As

We have studied growth and properties of quaternary alloy magnetic semiconductor (InGaMn)As grown both on GaAs substrates and on InP substrates by low-temperature molecular-beam epitaxy (LT-MBE). (InGaMn)As thin films were ferromagnetic below ~30 K, exhibiting strong magneto-optical effect. The lattice constant of [(InyGa1-y)1-xMnx]As, whose Mn concentration x is below 4%, is slightly smaller than that of InyGa1-yAs with the same In/Ga content ratio. We have also obtained very smooth surface morphology of nearly lattice matched (InGaMn)As thin films grown on InP substrates, which is important for application to thin-film type magneto-optical devices integrated with III-V opto-electronics.

cond-mat.mtrl-sci↗