Zhiyu Liu

Very high spin polarization in GaAs by injection from a (Ga,Mn)As Zener diode

We demonstrate an electrically injected electron spin polarization in GaAs of 80% at 4.6 K by interband tunneling from the valence band of (Ga,Mn)As into an (Al,Ga)As light-emitting diode. The polarization is analyzed by the oblique Hanle effect and vanishes at 120 K, the Curie temperature of the (Ga,Mn)As injector. The temperature and the bias dependence of the polarization are explained in terms of the properties of the (Ga,Mn)As/GaAs diode.

Technology and materials issues in semiconductor-based magnetoelectronics

There has been an increased interest in the introduction of magnetic thin films into semiconductors. This interest is motivated by the benefit found in using the magnetic thin-film properties (giant or tunnelling magnetoresistance and hysteresis) in magnetic memory (MRAM) products. Furthermore, the use of the electron spin in electronic, spintronic devices requires intimate ferromagnetic/semiconductor combinations. We review the technology and materials aspects of both the MRAM and spintronics fields that highlight the challenges that must be overcome in order to make magnetic (multilayer) films a standard ingredient in future electronics.

Hybrid epitaxial structures for spintronics

The use of electron spin in future spintronic applications requires hybrid ferromagnetic/semiconductor structures with well controlled materials properties. Besides the control of the magnetic properties there are strict requirements for the material aspects of these devices: single phase, single crystal, perfect interfaces, defect control. Molecular beam epitaxy (MBE) has been used very successfully over the past 10 years to produce the most interesting spintronic heterostructures. In this paper we review our effort in using MBE to fabricate spintronic materials and heterostructures. We also discuss some aspects of future spintronic devices with the focus on the material aspects of transferring the electron spin information from the magnetic side of the heterostructure into the semiconductor side.

Growth and characterization of Al1−XMnXas (X⩽4%) magnetic semiconductor: thin film and superlattices

Abstract A new diluted magnetic semiconductor, AlMnAs, was grown using stoichiometric low-temperature molecular beam epitaxy, with Mn composition up to 4%. In situ (RHEED) and ex situ (XRD, SIMS) characterization of uniform thin films and a GaAs/AlMnAs superlattice revealed good crystal quality and a very high Mn incorporation. Magnetic and electrical characterization showed the samples to be semi-insulating and hence paramagnetic, due to the lack of free carriers. The magnetic moment can be explained assuming Mn 2+ in the AlMnAs.

Growth and tunneling spectroscopy study of Fe/(GaAs, AlAs)/Ga1-xMnxAs ferromagnet/semiconductor heterostructures

Abstract Fully expitaxial tunneling structure Fe/Semiconductor/(Ga,Mn)As was grown and investigated. With semi-insulating (Ga,Mn)As as electrode, strong temperature dependent structure was observed in I–V characteristic. The electronic band structure in the contact region is discussed and the result is explained as inelastic tunneling via impurity states.

Magnetic interaction in two-dimensional AlMnAs/GaAs magnetic semiconductor heterostructures

Summary form only given. The incorporation of magnetic semiconductors in two-dimensional heterostructures enables to reveal the interaction mechanism between the magnetic impurities and the electronic carriers as well as offering an option to intriguing device applications in the spintronics area. We fabricated GaAs/AlAs heterostructures in which a two-dimensional hole gas (2DHG) is formed on the GaAs-side of the interface. In these heterostructures Mn-impurities were incorporated to realize samples with the following structures: GaAs//spl delta/-layer Mn (4.5% ML equivalent)/Al/sub 097/Mn/sub 003/As.