There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in heterostructures with AlGaN barrier layers of different Al concentrations (0.15<x<0.5) and thickness between 20 and 65 nm demonstrate the important role of spontaneous and piezoelectric polarization on the carrier confinement at GaN/AlGaN and AlGaN/GaN interfaces. Characterization of the electrical properties of nominally undoped transistor structures reveals the presence of high sheet carrier concentrations, increasing from 6×1012 to 2×1013 cm−2 in the GaN channel with increasing Al-concentration from x=0.15 to 0.31. The observed high sheet carrier concentrations and strong confinement at specific interfaces of the N- and Ga-face pseudomorphic grown heterostructures can be explained as a consequence of interface charges induced by ...

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Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures

Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.

/pdf/the-emergence-of-spin-electronics-in-data-storage-1vrnm5549k.pdf

The emergence of spin electronics in data storage

The fabrication methods of the microelectronics industry have been refined to produce ever smaller devices, but will soon reach their fundamental limits. A promising alternative route to even smaller functional systems with nanometre dimensions is the autonomous ordering and assembly of atoms and molecules on atomically well-defined surfaces. This approach combines ease of fabrication with exquisite control over the shape, composition and mesoscale organization of the surface structures formed. Once the mechanisms controlling the self-ordering phenomena are fully understood, the self-assembly and growth processes can be steered to create a wide range of surface nanostructures from metallic, semiconducting and molecular materials.

/pdf/engineering-atomic-and-molecular-nanostructures-at-surfaces-2sqr7sjd15.pdf

Engineering atomic and molecular nanostructures at surfaces

“Spintronics,” in which both the spin and charge of electrons are used for logic and memory operations, promises an alternate route to traditional semiconductor electronics. A complete logic architecture can be constructed, which uses planar magnetic wires that are less than a micrometer in width. Logical NOT, logical AND, signal fan-out, and signal cross-over elements each have a simple geometric design, and they can be integrated together into one circuit. An additional element for data input allows information to be written to domain-wall logic circuits.

http://science.sciencemag.org/content/sci/309/5741/1688.full.pdf

Magnetic Domain-Wall Logic

The authors present a 2.5-fold increase in the open-circuit voltage response of antenna-coupled nanothermocouples (ACNTCs) by thermally insulating them from the SiO2/Si substrate using an oxide membrane suspended over a cavity formed from the Si substrate. Polarization-dependent measurements are presented and compared to simulation results. The thermal response of the ACNTCs increases 2.5-fold when they are thermally insulated from the substrate by the cavity. The authors also show that the polarization-dependent response, and hence the polarization ratio, depends on the depth of the cavity.The authors present a 2.5-fold increase in the open-circuit voltage response of antenna-coupled nanothermocouples (ACNTCs) by thermally insulating them from the SiO2/Si substrate using an oxide membrane suspended over a cavity formed from the Si substrate. Polarization-dependent measurements are presented and compared to simulation results. The thermal response of the ACNTCs increases 2.5-fold when they are thermally insulated from the substrate by the cavity. The authors also show that the polarization-dependent response, and hence the polarization ratio, depends on the depth of the cavity.

Response increase of antenna-coupled nanothermocouples by thermal insulation

A novel process for silicon single electron transistors (Si-SET) is presented, combining chemical mechanical polishing (CMP) with the advantages of silicon processing. To eliminate effects caused by random distribution of dopants in the island, The Si-SET’s doped-Si island is replaced with an aluminum or tantalum island by integrating a metal CMP technique with our nano-encapsulation process. The fabricated hybrid Al-island Si-SET has ∼10 nm silicon on insulator lines as the source and drain leads. It shows characteristic Coulomb blockade oscillations with a charging energy of ∼4 meV. The fabrication results demonstrate the scalability of the SET island and the tunnel junction size in a manufacturable top-down approach.

Fabrication of hybrid metal island/silicon single electron transistor

Quantum-dot Cellular Automata (QCA) is a device architecture that uses the position of electrons in quantum-dot arrays to implement digital logic. We present the experimental demonstration of a two-stage QCA shift register and an analysis of errors encountered in its operation.

Experimental demonstration of a QCA shift register and analysis of errors

Single-electron tunneling transistors (SETs) and boxes (SEBs) exploit the phenomenon of Coulomb blockade to achieve unprecedented charge sensitivities. Single-electron boxes, however, despite their simplicity compared to SETs, have rarely been used for practical applications. The main reason for that is that unlike a SET where the gate voltage controls conductance between the source and the drain, an SEB is a two terminal device that requires either an integrated SET amplifier or high-frequency probing of its complex admittance by means of radio frequency reflectometry (RFR). The signal to noise ratio (SNR) for a SEB is small, due to its much lower admittance compared to a SET and thus matching networks are required for efficient coupling ofSEBs to an RFR setup. To boost the signal strength by a factor of N (due to a random offset charge) SEBs can be connected in parallel to form arrays sharing common gates and sources. The smaller the size of the SEB, the larger the charging energy of a SEB enabling higher operation temperature, and using devices with a small footprint ( 1000) can be assembled into an array occupying just a few square microns. We show that it is possible to design SEB arrays that may compete with an SET in terms of sensitivity. In this, we tested SETs using RF reflectometry in a configuration with no DC through path (“DC-decoupled SET” or DCD SET) along with SEBs connected to the same matching network. The experiment shows that the lack of a path for a DC current makes SEBs and DCD SETs highly electrostatic discharge (ESD) tolerant, a very desirable feature for applications. We perform a detailed analysis of experimental data on SEB arrays of various sizes and compare it with simulations to devise several ways for practical applications of SEB arrays and DCD SETs.

Radio Frequency Reflectometry of Single-Electron Box Arrays for Nanoscale Voltage Sensing Applications

We report on the polarization-dependent response of antenna-coupled single-metal thermocouples for infrared (IR) detection. We find that for certain antenna geometries, the observed open-circuit voltage response changes polarity as a function of the polarization angle of the incident radiation. This behavior is due to a change in the location of the hot junction as the polarization of the incident IR radiation rotates from the co-polarized to the cross-polarized state.

Alexei O. Orlov

Papers

Response increase of antenna-coupled nanothermocouples by thermal insulation

Fabrication of hybrid metal island/silicon single electron transistor

Experimental demonstration of a QCA shift register and analysis of errors

Radio Frequency Reflectometry of Single-Electron Box Arrays for Nanoscale Voltage Sensing Applications

Polarization-dependent response of antenna-coupled single-metal thermocouples