K. Ploog

Direct measurement of local lattice distortions in strained layer structures by HREM

Abstract We present a method which allows the direct measurement of local displacements within a crystal lattice by high-resolution electron microscopy (HREM). The basic idea of this method is the formation of moire structures when two two-dimensional lattices are superimposed. The first lattice is given by the experimental micrograph and the second one is calculated from an undisturbed area of the first. From the analysis of the resulting moire structure the local displacements of the crystal lattice with respect to the calculated lattice are deduced. We thus measure strain (which is characteristic for each element embedded in the host lattice) and thickness of the strained layers independently. Simultaneously, the positions of the interfaces are identified, without relying on the contrast difference between the constituent materials. Therefore, this novel method represents a chemical mapping which is inherently free of contrast interpretations.

In‐plane‐gated quantum wire transistor fabricated with directly written focused ion beams

A new unipolar electronic device with a quasi‐one‐dimensional (1D) tunable carrier channel defined by directly written focused ion beams has been fabricated and characterized. Special features of the device are simple and rapid fabrication in one single technology step, inherent self‐alignment, and linear instead of planar gates with very low capacitances. High integration as well as ultrahigh speed operation in logical and linear applications are feasible. The striking new aspect of this in‐plane‐gate structure is that the confining electric field is parallel to the two‐dimensional electron gas, and the distorted, insulating region serves as a dielectric. Ballistic 1D transport is observed at low temperatures, and field‐effect transistor operation of the device is demonstrated up to room temperature.

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.

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

Two-dimensional magneto-quantum transport on GaAs-AlxGa1-xAs heterostructures under non-ohmic conditions

\mathrm{GaN}:\mathrm{Gd}

Fundamental studies and device application of δ-doping in GaAs Layers and in AlxGa1−xAs/GaAs heterostructures

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

Optical phonons of hexagonal and cubic GaN studied by infrared transmission and Raman spectroscopy

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

Proposal of novel electron wave coupled devices

to

Subband physics for a “realistic” δ-doping layer

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

Magnetic structure of epitaxially grown MnAs on GaAs(001)

. The structural properties of these layers are found to be identical to those of undoped GaN layers. However, the magnetic characterization reveals an unprecedented effect. The average value of the magnetic moment per Gd atom is found to be as high as