Bernd Beschoten

Electrical spin injection in a ferromagnetic semiconductor heterostructure

Conventional electronics is based on the manipulation of electronic charge. An intriguing alternative is the field of ‘spintronics’, wherein the classical manipulation of electronic spin in semiconductor devices gives rise to the possibility of reading and writing non-volatile information through magnetism. Moreover, the ability to preserve coherent spin states in conventional semiconductors and quantum dots may eventually enable quantum computing in the solid state. Recent studies have shown that optically excited electron spins can retain their coherence over distances exceeding 100 micrometres (ref. 7). But to inject spin-polarized carriers electrically remains a formidable challenge. Here we report the fabrication of all-semiconductor, light-emitting spintronic devices using III–V heterostructures based on gallium arsenide. Electrical spin injection into a non-magnetic semiconductor is achieved (in zero magnetic field) using a p-type ferromagnetic semiconductor as the spin polarizer. Spin polarization of the injected holes is determined directly from the polarization of the emitted electroluminescence following the recombination of the holes with the injected (unpolarized) electrons.

Ultrahigh-mobility graphene devices from chemical vapor deposition on reusable copper

A novel dry transfer technique opens the door to large-scale CVD graphene with carrier mobilities of up to several 100,000 cm2 V−1 s−1. Graphene research has prospered impressively in the past few years, and promising applications such as high-frequency transistors, magnetic field sensors, and flexible optoelectronics are just waiting for a scalable and cost-efficient fabrication technology to produce high-mobility graphene. Although significant progress has been made in chemical vapor deposition (CVD) and epitaxial growth of graphene, the carrier mobility obtained with these techniques is still significantly lower than what is achieved using exfoliated graphene. We show that the quality of CVD-grown graphene depends critically on the used transfer process, and we report on an advanced transfer technique that allows both reusing the copper substrate of the CVD growth and making devices with mobilities as high as 350,000 cm2 V–1 s–1, thus rivaling exfoliated graphene.

Origin of high-temperature ferromagnetism in (Ga,Mn)N layers grown on 4H–SiC(0001) by reactive molecular-beam epitaxy

We report on the growth, structural as well as magnetic characterization of (Ga,Mn)N epitaxial layers grown directly on 4H–SiC(0001) by reactive molecular-beam epitaxy. We focus on two layers grown under identical conditions except for the Mn/Ga flux ratio. Structural characterization reveals that the sample with the lower Mn content is a uniform alloy, while in the layer with the higher Mn content, Mn-rich clusters are found to be embedded in the (Ga,Mn)N alloy matrix. Although the magnetic behavior of both the samples is similar at low temperatures, showing antiferromagnetic characteristics with a spin-glass transition, the sample with higher Mn content additionally exhibits ferromagnetic properties at and above room temperature. This ferromagnetism most likely originates from the Mn-rich clusters in this sample.

Toward Wafer Scale Fabrication of Graphene Based Spin Valve Devices

We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications.

Gd-doped GaN: A very dilute ferromagnetic semiconductor with a Curie temperature above 300 K

We present a systematic study of growth, structural, and magnetic characterization of

Raman spectroscopy as probe of nanometre-scale strain variations in graphene.

\mathrm{GaN}:\mathrm{Gd}

Nanosecond spin lifetimes in single- and few-layer graphene-hBN heterostructures at room temperature.

layers grown directly on 6H-SiC(0001) substrates by reactive molecular-beam epitaxy with a Gd concentration ranging from

Spin Lifetimes Exceeding 12 ns in Graphene Nonlocal Spin Valve Devices

7\ifmmode\times\else\texttimes\fi{}{10}^{15}

Ballistic Transport Exceeding 28 μm in CVD Grown Graphene

to

Role of MgO barriers for spin and charge transport in Co/MgO/graphene nonlocal spin-valve devices

2\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}