arXiv subjects

Philippe Dollfus

Publications and source records attributed to Philippe Dollfus.

27 records · Page 2Linked to original sources

arXiv2013

Improved performance of graphene transistors by strain engineering

By means of numerical simulation, we study in this work the effects of uniaxial strain on transport properties of strained graphene heterojunctions and explore the possibility to achieve good performance of graphene transistors using these hetero-channels. It is shown that a finite conduction-gap can open in the strain junctions due to the strain-induced deformation of graphene bandstructure. These hetero-channels are then demonstrated to improve significantly the operation of graphene field-effect-transistors (FETs). In particular, ON/OFF current ratio can reach a value of over 10$^5$. In graphene normal FETs, transconductance, though reduced compared to the case of unstrained devices, is still high while good saturation of current can be obtained. This results in high voltage gain and high transition frequency of a few hundreds of GHz for a gate length of 80 nm. In graphene tunneling FETs, subthreshold swing lower than 30 mV/dec, strong non-linear effects such as gate controllable negative differential conductance, and current rectification are observed.

cond-mat.mes-hall↗

arXiv2013

Interplay between Aharonov-Bohm interference and parity selective tunneling in zigzag graphene nanoribbon rings

We report a numerical study on Aharonov-Bohm (AB) effect and parity selective tunneling in pn junctions based on zigzag graphene nanoribbon rings. We find that when applying a magnetic field to the ring, the AB interference can reverse the parity symmetry of incoming waves and hence can strongly modulate the parity selective transmission through the system. Therefore, the transmission between two states of different parity exhibits the AB oscillations with a π-phase shift, compared to the case of states of same parity. On this basis, it is shown that interesting effects such as giant (both positive and negative) magnetoresistance and strong negative differential conductance can be achieved in this structure. Our study thus presents a new property of the AB interference, which could be helpful to further understand the transport properties of graphene mesoscopic-systems.

cond-mat.mes-hall↗

arXiv2013

Aharonov-Bohm effect and giant magnetoresistance in graphene nanoribbon rings

We report a numerical study on Aharonov-Bohm (AB) effect and giant magnetoresistance in rectangular rings made of graphene nanoribbons (GNRs). We show that in low energy regime where only the first subband of contact GNRs contributes to the transport, the transmission probability can be strongly modulated, i.e., almost fully suppressed, when tuning a perpendicular magnetic field. On this basis, strong AB oscillations with giant negative magnetoresistance can be achieved at room temperature. The magnetoresistance reaches thousands % in perfect GNR rings and a few hundred % with edge disordered GNRs. The design rules to observe such strong effects are also discussed. Our study hence provides guidelines for further investigations of the AB interference and to obtain high magnetoresistance in graphene devices.

cond-mat.mes-hall↗

arXiv2012

Disorder effects on energy bandgap and electronic transport in graphene-nanomesh-based structures

Using atomistic quantum simulation based on a tight binding model, we investigate the formation of energy gap Eg of graphene nanomesh (GNM) lattices and the transport characteristics of GNM-based electronic devices (single potential barrier structure and p-n junction) taking into account the atomic edge disorder of holes. We find that the sensitivity of Eg to the lattice symmetry (i.e., the lattice orientation and the hole shape) is significantly suppressed in the presence of the disorder. In the case of strong disorder, the dependence of Eg on the neck width is fitted well with the scaling rule observed in experiments [Liang et al., Nano Lett. 10, 2454 (2010)]. Considering the transport characteristics of GNM-based structures, we demonstrate that the use of finite GNM sections in the devices can efficiently improve their electrical performance (i.e., high ON/OFF current ratio, good current saturation and negative differential conductance behaviors). Additionally, if the length of GNM sections is appropriately limited, the detrimental effects of disorder on transport can be avoided to a large extent. Our study provides a good explanation of the available experimental data on GNM energy gap and should be helpful for further investigations of GNM-based devices.

cond-mat.mes-hall↗

arXiv2012

Resonant tunneling diode based on graphene/h-BN heterostructure

In this letter, we propose the resonant tunneling diode (RTD) based on a double-barrier graphene/boron nitride (BN) heterostructure as device suitable to take advantage of the elaboration of atomic sheets containing different domains of BN and C phases within a hexagonal lattice. The device operation and performance are investigated by means of a self- consistent model within the non-equilibrium Green's function formalism on a tight-binding Hamiltonian. This RTD exhibits a negative differential conductance effect which involves the resonant tunneling through both the electron and hole bound states of the graphene quantum well. It is shown that the peak- to-valley ratio can reach the value of 4 at room temperature for gapless graphene and the value of 13 for a bandgap of 50 meV.

cond-mat.mes-hall↗

arXiv2006

Transport and noise in resonant tunneling diode using self-consistent Green function calculation

The fully self-consistent non-equilibrium Green functions (NEGFs) approach to the quantum transport is developed for the investigation of one-dimensional nano-scale devices. Numerical calculations performed for resonant tunneling diodes (RTDs) of different designs and at different temperatures show reasonable results for the potential and electron density profiles, as well as for the transmission coeffcient and the current-voltage characteristics. The resonant behavior is discussed in detail with respect to the quantum-well width, the barrier thickness, and the temperature. It is also shown that within the framework of approach used the current noise spectral density can be straightforwardly calculated for both the coherent and the sequential tunneling models. In qualitative agreement with experiments, obtained results highlight the role of charge interaction which causes a fluctuation of density of states in the well and therefore a noise enhancement in the negative differential conductance region.

cond-mat.mes-hall↗

arXiv2005

Shot noise in metallic double dot structures with a negative differential conductance

The shot noise of current through a metallic double quantum dot structure exhibiting negative differential conductance is studied. We can exactly solve the master equation and derive an analytical expression of the spectral density of current fluctuations as a function of frequency in the first Coulomb staircase region. For a large range of bias voltage the noise is calculated by Monte Carlo simulation. We show that the noise is always sub-Poissonian though it is considerably enhanced in the negative differential conductance regime.

cond-mat.mes-hall↗

arXiv2005

From wave-functions to current-voltage characteristics: overview of a Coulomb blockade device simulator using fundamental physical parameters

The purpose of this article is to present an accurate way, based on a physical description, to simulate Coulomb blockade devices. The method underlying the simulations depends only on fundamental parameters of the system and does not require the use of high level fitting parameters as tunneling conductances contrary to number of current Coulomb blockade simulators. It lies mainly on the transfer Hamiltonian formalism and Bardeen's formula within the framework of effective mass tensor. It can be applied to metallic Coulomb blockade devices as well as semiconductor ones. The details of this method are extensively reviewed from a theoretical point of view and the main results are presented. In particular, we study how to obtain tunneling rates information to deduce current/voltage characteristics of Metal-Insulator-Metal-Insulator-Metal (MIMIM) and Metal-Insulator-Si Quantum Dot-Insulator-Metal (MISiIM) structures.

cond-mat.mes-hall↗

arXiv2003

Exact calculation of single-electron states in Si-nanocrystal embedded in SiO2

We present an exact calculation of the single-electron energies and wave-functions for any bound state in a realistic Si-SiO2 spherical quantum dot, including the material dependence of the electron effective mass. The influence of dot radius, confinement barrier potential and barrier-to-dot electron mass ratio on the electronic structure is investigated in detail. The results show that the energy structure shifts down from some tens to some hundreds meV compared to that obtained in the simplified model where the change in effective mass is neglected. Our exact single-electron calculation is finally used to verify the accuracy of the results obtained from a numerical approximate method developed to treat many-electron systems.

cond-mat.mtrl-sci↗