Alexei O. Orlov

Electron transport in AlGaN–GaN heterostructures grown on 6H–SiC substrates

We investigated two-dimensional electron transport in doped AlGaN–GaN heterostructures (with the electron sheet concentration ns≈1013 cm−2) grown on conducting 6H–SiC substrates in the temperature range T=0.3–300 K. The electron mobility in AlGaN–GaN heterostructures grown on SiC was higher than in those on sapphire substrates, especially at cryogenic temperatures. The highest measured Hall mobility at room temperature was μH=2019 cm2/V s. At low temperatures, the electron mobility increased approximately five times and saturated below 10 K at μH=10250 cm2/V s. The experimental results are compared with the electron mobility calculations accounting for various electron scattering mechanisms.We investigated two-dimensional electron transport in doped AlGaN–GaN heterostructures (with the electron sheet concentration ns≈1013 cm−2) grown on conducting 6H–SiC substrates in the temperature range T=0.3–300 K. The electron mobility in AlGaN–GaN heterostructures grown on SiC was higher than in those on sapphire substrates, especially at cryogenic temperatures. The highest measured Hall mobility at room temperature was μH=2019 cm2/V s. At low temperatures, the electron mobility increased approximately five times and saturated below 10 K at μH=10250 cm2/V s. The experimental results are compared with the electron mobility calculations accounting for various electron scattering mechanisms.

Experimental demonstration of a binary wire for quantum-dot cellular automata

Experimental studies are presented of a binary wire based on the quantum-dot cellular automata computational paradigm. The binary wire consists of capacitively coupled double-dot cells charged with single electrons. The polarization switch caused by an applied input signal in one cell leads to the change in polarization of the adjacent cell and so on down the line, as in falling dominos. Wire polarization was measured using single islands as electrometers. Experimental results are in very good agreement with the theory and confirm there are no metastable states in the wire.

Operation of a quantum-dot cellular automata (QCA) shift register and analysis of errors

Quantum-dot cellular automata (QCA) is a digital logic architecture that uses single electrons in arrays of quantum dots to perform binary operations. A QCA latch is an elementary building block which can be used to build shift registers and logic devices for clocked QCA architectures. We discuss the operation of a QCA latch and a shift register and present an analysis of the types and properties of errors encountered in their operation.

Experimental demonstration of a leadless quantum-dot cellular automata cell

We present the experimental characterization of a leadless (floating) double-dot system and a leadless quantum-dot cellular automata cell, where aluminum metal islands are connected to the environment only by capacitors. Here, single electron charge transfer can be accomplished only by the exchange of an electron between the dots. The charge state of the dots is monitored using metal islands configured as electrometers. We show improvements in the cell performance relative to leaded dots, and discuss possible implications of our leadless design to the quantum-dot cellular automata logic implementation.

Experimental demonstration of clocked single-electron switching in quantum-dot cellular automata

A device representing a basic building block for clocked quantum-dot cellular automata architecture is reported. Our device consists of three floating micron-size metal islands connected in series by two small tunnel junctions where the location of an excess electron is defined by electrostatic potentials on gates capacitively coupled to the islands. In this configuration, the middle dot acts as an adjustable Coulomb barrier allowing clocked control of the charge state of the device. Charging diagrams of the device show the existence of several operational modes, in good agreement with theory. The clocked switching of a single electron is experimentally demonstrated and advantages of this architecture are discussed.

Quantum-dot cellular automata: computing with coupled quantum dots

We discuss novel nanoelectronic architecture paradigms based on cells composed of coupled quantum-dots. Boolean logic functions may be implemented in specific arrays of cells representing binary information, the so-called quantum-dot cellular automata (QCA). Cells may also be viewed as carrying analogue information and we outline a network-theoretic description of such quantum-dot nonlinear networks (Q-CNN). In addition, we discuss possible realizations of these structures in a variety of semiconductor systems (including GaAs/AlGaAs, Si/SiGe, and Si/SiO2), rings of metallic tunnel junctions, and candidates for molecular implementations. We report the experimental demonstration of all the necessary elements of a QCA cell, including direct measurement of the charge polarization of a double-dot system, and direct control of the polarization of those dots via single electron transitions in driver dots. Our experiments are the first demonstration of a single electron controlled by single electrons.

Quantum-dot cellular automata: Review and recent experiments (invited)

An introduction to the operation of quantum-dot cellular automata is presented, along with recent experimental results. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. The operation of this basic cell is confirmed by the externally controlled polarization change of the cell.

Demonstration of a six-dot quantum cellular automata system

We report an experimental demonstration of a logic cell for quantum-dot cellular automata (QCA). This nanostructure-based computational paradigm allows logic function implementation without the use of transistors. The four-dot QCA cell is defined by a pair of series-connected double dots, and the coupling between the input and the output double dots is provided by lithographically defined capacitors. We demonstrate that, at low temperature, an electron switch in the input double dot induces an opposite electron switch in the output double dot, resulting in a polarization change of the QCA cell. Switching is verified from the electrometer signals, which are coupled to the output double dot. We perform theoretical simulations of the device characteristics and find excellent agreement with theory.

Power gain in a quantum-dot cellular automata latch

We present an experimental demonstration of power gain in quantum-dot cellular automata (QCA) devices. Power gain is necessary in all practical electronic circuits where power dissipation leads to decay of logic levels. In QCA devices, charge configurations in quantum dots are used to encode and process binary information. The energy required to restore logic levels in QCA devices is drawn from the clock signal. We measure the energy flow through a clocked QCA latch and show that power gain is achieved.

Quantum-dot cellular automata

An introduction to the operation of quantum-dot cellular automata (QCA) is presented, along with recent experimental results. QCA is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. A noninvasive electrometer is presented which improves the sensitivity and linearity of dot potential measurements. The operation of this basic cell is confirmed by an externally controlled polarization change of the cell.