Pham Nam Hai

Electron effective mass (me*) in GaNxAs1−x/GaAs quantum wells (QWs) is investigated by the optically detected cyclotron resonance technique. The me* values of 0.12m0 and 0.19m0 are directly determined for the 70-Å-thick QWs with N composition of 1.2% and 2.0%, respectively. This sizable increase in the electron effective mass is consistent with the earlier theoretical predictions based on the strong interaction of the lowest conduction band states with the upper lying band states or impurity ban

We show that by introducing isoelectronic iron (Fe) magnetic impurities and Beryllium (Be) double-donor atoms into InAs, it is possible to grow an n-type ferromagnetic semiconductor (FMS) with the ability to control ferromagnetism by both Fe and independent carrier doping by low-temperature molecular-beam epitaxy. We demonstrate that (In,Fe)As doped with electrons behaves as an n-type electron-induced FMS. This achievement opens the way to realize spin-devices such as spin light-emitting diodes

The electron effective mass (m*) in n-type carrier-induced ferromagnetic semiconductor (In,Fe)As was estimated by using the thermoelectric Seebeck effect. It was found that m* is 0.03 ∼ 0.17m0 depending on the electron concentration, where m0 is the free electron mass. These values are similar to those of electrons in the conduction band of n+ InAs. The Fermi level EF in (In,Fe)As is located at least 0.15 eV above the conduction band bottom. Our results indicate that electron carriers in (In,Fe)

Abstract We report on the growth and characterization of BiSb thin films deposited on sapphire substrates by sputtering deposition with Ar and Kr plasma. By optimizing the growth conditions, we are able to obtain quasi-single-crystal BiSb(001) thin films with equivalent twin crystals. The conductivity of BiSb at the studied thicknesses exceeds 10 5 Ω −1 m −1 , reaching 1.8 × 10 5 Ω −1 m −1 at 10 nm. From the temperature dependence of the electrical resistivity, we confirm the existence of metall

The giant spin Hall effect (SHE) in topological insulators (TIs) is very attractive for applications to various spintronic devices, notably spin-orbit torque magnetoresistive random-access memory (SOT-MRAM). In this paper, we review the recent progress on the giant SHE in TIs, with emphasis on the role of topological surface states. We discuss current challenges and future prospects for TIs as a realistic material in SOT-MRAM.

Topological insulators (TIs) are promising for efficient spin current sources in spin–orbit torque (SOT) magnetoresistive random access memory (MRAM). However, TIs are usually deposited by molecular beam epitaxy on single crystalline III–V semiconductor or sapphire substrates, which are not suitable for realistic applications. Here, we studied SOT characteristics in sputtered BiSb topological insulator—Pt/Co/Pt—MgO heterostructures deposited on oxidized Si substrates, where Pt/Co/Pt trilayers ha

Topological materials, such as topological insulators (TIs), have great potential for ultralow power spintronic devices, thanks to their giant spin Hall effect. However, the giant spin Hall angle (θ_SH > 1) is limited to a few chalcogenide TIs with toxic elements and low melting points, making them challenging for device integration during the silicon Back-End-of-Line (BEOL) process. Here, we show that by using a half-Heusler alloy topological semi-metal (HHA-TSM), YPtBi, it is possibl

We investigate the thermodynamics of phase decomposition in magnetic alloy semiconductors (MASs) using the statistical Flory–Huggins lattice model. Based on this model, we propose a method to determine experimentally the interaction parameter χ and apply it to draw the phase decomposition diagram of (GaMn)As. The interaction energy of (GaMn)As was estimated to be about 5.7 mRy, which is close to the first principle calculation of 4.2 mRy. Using this phase diagram, we fabricated MnAs nanoparticle

Topological insulators (TIs) are promising for spin–orbit torque (SOT) switching thanks to their giant spin Hall angle. SOT switching using TIs has been studied so far in the thermal activation regime by direct currents or relatively long pulse currents (≥10 ns). In this work, we studied SOT magnetization switching of (Pt/Co) multilayers with strong perpendicular magnetic anisotropy by the BiSb topological insulator in both thermal activation and fast switching regime with pulse width down to 1

The authors have investigated tunneling magnetoresistance (TMR) of magnetic tunnel junctions (MTJs) consisting of MnAs thin film (20nm)∕GaAs(1nm)∕AlAs(d=2–5nm)∕GaAs:MnAs nanoclusters (10nm). The GaAs:MnAs material contains ferromagnetic MnAs nanoclusters in a GaAs matrix and acts as a spin injector and a spin detector. They observed an oscillatory behavior of the TMR ratio with the increasing AlAs barrier thickness, which can be explained by the quantum interference of two X-valley related wave

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 NiAs-type hexagonal 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 transpo