arXiv subjects

Mircea Dragoman

Publications and source records attributed to Mircea Dragoman.

17 recordsLinked to original sources

arXiv2019

Graphene bandgap induced by ferroelectric Pca2$_1$ HfO$_2$ substrate: a first-principles study

The electronic properties of graphene on top of ferroelectric HfO$_2$ substrates in orthorhombic phase with space group Pca2$_1$ are investigated using density functional theory calculations. The space group Pca2$_1$ was recently identified as one of the two potential candidates for ferroelectricity in hafnia, with the polarization direction oriented along [001] direction. Our results indicate the appearance of sizable energy gaps in graphene induced by the HfO$_2$ substrate, as a consequence of orbital hybridization and locally deformed graphene structure. The gap sizes depend on the type of the HfO$_2$ terminations interacting with graphene, showing larger gaps for oxygen terminated slabs compared to hafnium terminated ones. These observations may prove to be highly significant for the development of graphene based field effect transistors using high-k dielectrics.

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arXiv2018

Wafer-scale fabrication and room-temperature experiments on graphene-based gates for quantum computation

We have fabricated at wafer scale graphene-based configurations suitable for implementing at room temperature one-qubit quantum gates and a modified Deutsch-Jozsa algorithm. Our measurements confirmed the (quasi-)ballistic nature of charge carrier propagation through both types of devices, which have dimensions smaller than the room-temperature mean-free-path in graphene. As such, both graphene-based configurations were found to be suitable for quantum computation. These results are encouraging for demonstrating a miniaturized, room-temperature quantum computer based on graphene.

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arXiv2017

Solving the graphene electronics conundrum: high mobility and high on-off ratio in graphene nanopatterned transistors

Tens of graphene transistors with nanoperforated channels and different channel lengths were fabricated at the wafer scale. The nanoholes have a central diameter of 20 nm and a period of 100 nm, the lengths of the channel being of 1, 2, 4 or 8 micrometers. We have found that the mobility in these 2 micrometer-wide transistors varies from about 10400 cm2/Vs for a channel length of 1 micrometer to about 550 cm2/Vs for a channel length of 8 micrometer. Irrespective of the mobility value, in all transistors the on-off ratio is in the range 10^3-10^4 at drain and gate voltages less than 2 V. The channel length-dependent mobility and conductance values indicate the onset of strong localization of charge carriers, whereas the high on-off ratio is due to bandgap opening by nanoperforations.

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arXiv2016

Room temperature on-wafer ballistic graphene field-effect-transistor with oblique double-gate

We have fabricated and measured ballistic graphene transistors with two oblique gates that can be independently biased. The gate lengths are about 38 nm and are separated by a distance of 30 nm, the tilting angle being of 45o with respect to source and drain electrodes distanced at 190 nm. Electric measurements reveal specific properties of ballistic carrier transport, i.e. nonlinear drain voltage-drain current dependence, showing a saturation region, and negative differential resistance at certain bias voltages, which cannot be explained without physical mechanisms related to ballistic transport. Tens of ballistic transistors, with very large transconductances, were fabricated on a chip cut from a 4 inch graphene wafer. Such double-gate transistor configurations can be used also as extremely efficient, state-of-the-art photodetectors.

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arXiv2016

Memristive GaN ultrathin suspended membrane array

In this paper, we show that ultrathin GaN membranes having a thickness of 15 nm and planar dimensions of 12x184 microns act as memristive devices. This fact is due to the migration of the negatively charged deep traps, which form in the volume of the membrane during the fabrication process, towards the unoccupied surface states of the suspended membranes. The time constant of the migration process is of the order of tens of second and varies with the current or voltage sweep.

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arXiv2016

Room temperature nanostructured graphene transistors with high on-off ratio

We report the batch fabrication of graphene field-effect-transistors (GFETs) with nanoperforated graphene as channel. The transistors were cut and encapsulated. The encapsulated GFETs display saturation regions that can be tuned by modifying the top gate voltage, and have on/off ratios of up to 10^8 at room temperature. In addition, the nanoperforated GFETs display orders of magnitude higher photoresponses than any room-temperature graphene detector configurations that do not involve heterostructures with bandgap materials.

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arXiv2014

Two-and three-qubit room-temperature graphene quantum gates

Proposed configurations for the implementation of graphene-based CNOT and Toffoli gates working at room temperature are presented. These two logic gates, essential for any quantum computing algorithm, involve ballistic Y junctions for qubit implementation, quantum interference for qubit interaction and oblique gates for optimizing the output, and can be fabricated using existing nanolitographical techniques. The proposed configurations of CNOT and Toffoli quantum logic gates are based on the very large mean-free-paths of carriers in graphene at room temperature.

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arXiv2014

Enhanced architectures for room-temperature reversible logic gates in graphene

We show that reversible two- and three-input logic gates, among which we mention the universal Toffoli gate, can be implemented with three tilted gating electrodes patterned on a monolayer graphene flake. These low-dissipation gates are based on the unique properties of ballistic charge carriers in graphene, which induce the appearance of bandgaps in transmission for properly potential barriers. The enhanced architectures for reversible logic gate implementations proposed in this paper offer a remarkable design simplification in comparison to standard approaches based on field-effect transistor circuits and a potential high-frequency operation.

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arXiv2014

Complementary memristive device based on a thin film of MoS2 monolayers

In this manuscript we demonstrate experimentally that a thin film of MoS2 monolayers formed by drop-casting on a gold interdigitated electrode on Si/SiO2 behaves like a complementary memristive device, which is a key device of future crossbar memories. The hysteretic behavior of this device is modulated by light in a spectral range expanding from UV up to IR. In contrast to previous complementary memristive devices based on complicated oxides heterostructures, this device has a simple fabrication procedure and can be controlled by light, in addition to electrical signals.

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arXiv2014

Negative differential resistance in graphene-based ballistic field effect transistor with oblique top gate

Negative differential resistance (NDR) with room temperature peak-valley-ratio of 8 has been observed in a ballistic field-effect-transistor (FET) based on graphene, having an oblique top gate. Graphene FETs with a top gate inclination angle of 45 degrees and a drain-source distance of 400 nm were fabricated on a chip cut from a 4 inch graphene wafer grown by CVD. From the 60 measured devices, NDR was observed only in the regions where the CVD graphene displays the Raman signature of defectless monolayers. In other specific positions on the wafer, where graphene quality was not high enough and the Raman signature indicated the presence of defects, the ballistic character of transport is lost and the graphene FETs display nonlinear drain-voltage dependences tuned by the top and back gate voltage.

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arXiv2013

Microwave and millimeterwave electrical permittivity of graphene monolayer

The effective electrical permittivity of a graphene monolayer is experimentally investigated in the 5-40 GHz range, which encompasses the microwave and the lower part of millimeterwave spectrum. The measurements were carried out using a coupled coplanar waveguide placed over a graphene monolayer flake, which is deposited on Si/SiO2. In contrast to some initial predictions, the effective permittivity of the graphene monolayer is slightly decreasing in the above-mentioned frequency range and has an average value of 3.3.

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arXiv2012

Geometrical-induced rectification in two-dimensional ballistic nanodevices

The paper demonstrates that a two-dimensional ballistic nanodevice in which the electron gas satisfies either the Schroodinger equation (as in quantum wells in common semiconductor heterostructures) or the Dirac equation (as in graphene) is able to rectify an electric signal if the device has a non-uniform cross section, for instance a taper configuration. No p-n junctions or dissimilar electrodes are necessary for rectification.

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arXiv2012

Graphene radio: Detecting radiowaves with a single atom sheet

We present the experimental evidence of RF demodulation by a graphene monolayer embedded in a coplanar structure. The demodulator was tested in the frequency range from 100 MHz to 25 GHz using amplitude modulated input signals. An input power of 0 dBm (1 mW) was used which is the typical power emitted for short range wireless communication systems, such as Bluetooth. The graphene demodulator exhibits good signal response in the frequency range associated to industrial, scientific and medical (ISM) radio band (2.4 GHz).

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arXiv2011

Time Flow in Graphene and Its Implications on the Cutoff Frequency of Ballistic Graphene Devices

This manuscript deals with time flow in ballistic graphene devices. It is commonly believed that in the ballistic regime the traversal time of carriers in gated graphene at normal incidence is just the ratio of the length of the device and the Fermi velocity. However, we show that the traversal time is much slower if the influence of metallic contacts on graphene is considered. Even the transmission at normal incidence becomes smaller than 1, contradicting yet another common belief. These unexpected effects are due to the transformation of Schrodinger electrons in the metallic contact into Dirac electrons in graphene and vice versa. As a direct consequence of these transformations, the ultimate performance of gated ballistic devices are much lower than expected, in agreement with experimental results.

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arXiv2009

Real-Time Detection of Deoxyribonucleic Acid Bases via their Negative Differential Conductance Signature

In this paper we present a method for the real-time detection of the bases of the deoxyribonucleic acid using their signatures in negative differential conductance measurements. The present methods of electronic detection of deoxyribonucleic acid bases are based on a statistical analysis because the electrical currents of the four bases are weak and do not differ significantly from one base to another. In contrast, we analyze a device that combines the accumulated knowledge in nanopore and scanning tunneling detection, and which is able to provide very distinctive electronic signatures for the four bases.

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arXiv2007

Negative Differential Resistance of Electrons in Graphene Barrier

The graphene is a native two-dimensional crystal material consisting of a single sheet of carbon atoms. In this unique one-atom-thick material, the electron transport is ballistic and is described by a quantum relativistic-like Dirac equation rather than by the Schrodinger equation. As a result, a graphene barrier behaves very differently compared to a common semiconductor barrier. We show that a single graphene barrier acts as a switch with a very high on-off ratio and displays a significant differential negative resistance, which promotes graphene as a key material in nanoelectronics.

quant-ph↗

arXiv2007

Metamaterials for Ballistic Electrons

The paper presents a metamaterial for ballistic electrons, which consists of a quantum barrier formed in a semiconductor with negative effective electron mass. This barrier is the analogue of a metamaterial for electromagnetic waves in media with negative electrical permittivity and magnetic permeability. Besides applications similar to those of optical metamaterials, a nanosized slab of a metamaterial for ballistic electrons, sandwiched between quantum wells of positive effective mass materials, reveals unexpected conduction properties, e.g. single or multiple room temperature negative differential conductance regions at very low voltages and with considerable peak-to-valley ratios, while the traversal time of ballistic electrons can be tuned to larger or smaller values than in the absence of the metamaterial slab. Thus, slow and fast electrons, analogous to slow and fast light, occur in metamaterials for ballistic electrons.

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