Ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization. The material can be patterned using standard nanolithography methods. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. All-graphene electronically coherent devices and device architectures are envisaged.

https://science.sciencemag.org/content/sci/312/5777/1191.full.pdf

Electronic Confinement and Coherence in Patterned Epitaxial Graphene

http://absimage.aps.org/image/MAR07/MWS_MAR07-2006-006269.pdf

The surface and materials science of tin oxide

We review work on In2O3:Sn films prepared by reactive e‐beam evaporation of In2O3 with up to 9 mol % SnO2 onto heated glass. These films have excellent spectrally selective properties when the deposition rate is ∼0.2 nm/s, the substrate temperature is ≳150 °C, and the oxygen pressure is ∼5×10−4 Torr. Optimized coatings have crystallite dimensions ≳50 nm and a C‐type rare‐earth oxide structure. We cover electromagnetic properties as recorded by spectrophotometry in the 0.2–50‐μm range, by X‐band microwave reflectance, and by dc electrical measurements. Hall‐effect data are included. An increase of the Sn content is shown to have several important effects: the semiconductor band gap is shifted towards the ultraviolet, the luminous transmittance remains high, the infrared reflectance increases to a high value beyond a certain wavelength which shifts towards the visible, phonon‐induced infrared absorption bands vanish, the microwave reflectance goes up, and the dc resisitivity drops to ∼2×10−4 Ω cm. The corre...

Evaporated Sn‐doped In2O3 films: Basic optical properties and applications to energy‐efficient windows

The authors present experimental results, and a supporting theory, showing that a one-dimensional system in which transport is ballistic possesses a quantised resistance, h/2ie2, where i is the number of occupied 1D sub-bands and the spin degeneracy is two. A short narrow channel is defined in the 2DEG of a GaAs-AlGaAs heterojunction and as the width of the system is changed, the sub-bands pass through the Fermi energy and the resistance jumps between quantised values. The value of the quantised resistance is derived and the accuracy of the quantisation is discussed. The effect can be strong at temperatures approximately 0.1 K, with up to 17 sub-bands being observed. The action of a transverse magnetic field is to depopulate the sub-bands and form hybrid levels; a parallel field lifts the spin degeneracy and brings about a further quantisation of resistance at values h/2(i+1/2)e2.

https://iopscience.iop.org/article/10.1088/0022-3719/21/8/002/pdf

One-dimensional transport and the quantisation of the ballistic resistance

Films of ZnO:Al were produced by weakly reactive dual-target magnetron sputtering. Optical band gaps, evaluated from spectrophotometric data, were widened in proportion to the Al doping. The widening could be quantitatively reconciled with an effective-mass model for n-doped semiconductors, provided the polar character of ZnO was accounted for.

/pdf/band-gap-tailoring-of-zno-by-means-of-heavy-al-doping-395n8l1owb.pdf

Band-gap tailoring of ZnO by means of heavy Al doping

In this paper we investigate the optical properties of evaporated films of doped semiconducting In2O3 in the 2-6-eV range, i.e., around the fundamental bandgap. The study serves two main purposes: to elucidate basic properties of a heavily n-doped semiconductor, and to improve our understanding of a technologically important material which is widely used when transmittance of visible or solar radiation needs to be combined with good electrical conduction or low thermal emittance.

/pdf/band-gap-widening-in-heavily-sn-doped-in-2-o-3-2xb73ivcpq.pdf

Band-gap widening in heavily Sn-doped In 2 O 3

Band-gap narrowing in heavily doped many-valley semiconductors

We present results on the transverse magnetoconductance in the range 0.3 to 8 T of a narrow, variable-width channel in a GaAs:AlGaAs heterojunction. As the width of the channel is decreased below 0.25 \ensuremath{\mu}m the structure in the magnetoconductance changes from Shubnikov-de Haas oscillations to the magnetic depopulation of one-dimensional subbands. A semiclassical WKB calculation is presented which gives good agreement with experiment.

Karl-Fredrik Berggren

Papers

Band-gap tailoring of ZnO by means of heavy Al doping

Band-gap widening in heavily Sn-doped In 2 O 3

Band-gap narrowing in heavily doped many-valley semiconductors

Magnetic depopulation of 1D subbands in a narrow 2D electron gas in a GaAs:AlGaAs heterojunction.

Characterization of very narrow quasi-one-dimensional quantum channels