Possible conductance quantization in narrow wires with point-contact boundaries

The shot noise power spectrum of a quantum point contact structure is investigated based upon a time-dependent Landauer approach. The system is modeled by an open conducting channel coupled with two infinite reservoirs. When the channel length L ≫ ξ (the coherence length of an electron wave packet), all the channel states moving from source to drain are fully occupied while all the opposite ones are empty. Consequently, shot noise is suppressed to zero along with conductance quantization. For L ~ ξ, however, while the conductance is still well quantized, the shot noise is only partially suppressed to a nonzero fraction of its full level, in agreement with recent experimental data.

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Robust quantum point contact operation of narrow graphene constrictions patterned by AFM cleavage lithography

npj 2D Materials and Applications ◽

10.1038/s41699-020-00177-x ◽

2020 ◽

Vol 4 (1) ◽

Author(s):

Péter Kun ◽

Bálint Fülöp ◽

Gergely Dobrik ◽

Péter Nemes-Incze ◽

István Endre Lukács ◽

...

Keyword(s):

Magnetic Field ◽

Point Contact ◽

High Mobility ◽

Zero Magnetic Field ◽

High Symmetry ◽

Conductance Quantization ◽

Si Substrates ◽

Edge Quality ◽

Quantum Point ◽

Mechanical Cleavage

AbstractDetecting conductance quantization in graphene nanostructures turned out more challenging than expected. The observation of well-defined conductance plateaus through graphene nanoconstrictions so far has only been accessible in the highest quality suspended or h-BN encapsulated devices. However, reaching low conductance quanta in zero magnetic field, is a delicate task even with such ultra-high mobility devices. Here, we demonstrate a simple AFM-based nanopatterning technique for defining graphene constrictions with high precision (down to 10 nm width) and reduced edge-roughness (+/−1 nm). The patterning process is based on the in-plane mechanical cleavage of graphene by the AFM tip, along its high symmetry crystallographic directions. As-defined, narrow graphene constrictions with improved edge quality enable an unprecedentedly robust QPC operation, allowing the observation of conductance quantization even on standard SiO2/Si substrates, down to low conductance quanta. Conductance plateaus, were observed at n × e2/h, evenly spaced by 2 × e2/h (corresponding to n = 3, 5, 7, 9, 11) in the absence of an external magnetic field, while spaced by e2/h (n = 1, 2, 3, 4, 5, 6) in 8 T magnetic field.

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Valley polarized conductance quantization in bilayer graphene narrow quantum point contact

Applied Physics Letters ◽

10.1063/5.0052845 ◽

2021 ◽

Vol 118 (26) ◽

pp. 263102

Author(s):

Kohei Sakanashi ◽

Naoto Wada ◽

Kentaro Murase ◽

Kenichi Oto ◽

Gil-Ho Kim ◽

...

Keyword(s):

Point Contact ◽

Bilayer Graphene ◽

Quantum Point Contact ◽

Conductance Quantization ◽

Quantum Point

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BREAKDOWN MODES AND BREAKDOWN STATISTICS OF ULTRATHIN SiO2 GATE OXIDES

International Journal of High Speed Electronics and Systems ◽

10.1142/s0129156401001003 ◽

2001 ◽

Vol 11 (03) ◽

pp. 789-848 ◽

Cited By ~ 11

Author(s):

JORDI SUÑE ◽

DAVID JIMENEZ ◽

ENRIQUE MIRANDA

Keyword(s):

Dielectric Breakdown ◽

Point Contact ◽

Prevalence Ratio ◽

Oxide Thickness ◽

Cmos Technology ◽

Statistical Correlation ◽

Gate Insulator ◽

Conductance Quantization ◽

Common Framework ◽

Soft Breakdown

The dielectric breakdown of ultra-thin silicon dioxide films used as gate insulator in MOSFETs is one of the most important reliability issues in CMOS technology. In this paper, two main aspects of oxide breakdown are considered: the modeling of the breakdown statistics and the properties of the two main breakdown modes, namely Soft Breakdown and Hard Breakdown. The most invoked models for the breakdown statistics that relate defect generation and breakdown are reviewed. Particular attention is paid to the percolation models and to a recent cell-based analytic picture. The scaling of the breakdown distribution with oxide thickness is considered and it is shown that both pictures are equivalent for ultra-thin oxides. It is shown that soft and hard breakdown show coincident statistics and this is used to conclude that both breakdown models are triggered by the formation of the same kind of defect-related conduction paths. The big differences in the post-breakdown conduction properties are attributed to phenomena occurring during the very fast breakdown current runaway that determine the area of the final breakdown spot. The properties of soft and hard breakdown are explained within the common framework of a model based on quantum-point-contact conduction. This mesoscopic approach to the post-breakdown conduction is shown to explain the main experimental results including conductance quantization after hard breakdown, the area and thickness independence of the soft-breakdown I(V) characteristics and the statistical correlation between current level and normalized conductance. Finally, we deal with some open questions and relevant issues that are now subject of intensive investigations. The fact that some breakdown events can be tolerated for some digital applications is considered. In this regard, the distinction between breakdown and device failure distributions is made and some implications for device reliability are discussed. It is argued that energy dissipation during the breakdown runaway can determine the breakdown efficiency, the prevalence ratio of soft to hard breakdown, and their variations with stress conditions, experimental setup (series impedance) and sample characteristics.

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Двухканальный электронный транспорт в подвешенных квантовых точечных контактах с боковыми затворами

Физика и техника полупроводников ◽

10.21883/ftp.2020.12.50235.9512 ◽

2020 ◽

Vol 54 (12) ◽

pp. 1344

Author(s):

Д.А. Похабов ◽

А.Г. Погосов ◽

Е.Ю. Жданов ◽

А.К. Бакаров ◽

А.А. Шкляев

Keyword(s):

Electron Gas ◽

Point Contact ◽

Channel Structure ◽

Quantum Point Contact ◽

Dimensional Electron ◽

Conductance Quantization ◽

Quantum Point ◽

Dimensional Electron Gas ◽

Electrostatic Mechanism ◽

Double Channel

The conductance of a suspended quantum point contact fabricated from GaAs/AlGaAs heterostructures with a two-dimensional electron gas, equipped with the in-plane side gates separated from the constriction using lithographical trenches, is studied. The conductance as a function of the gate voltages demonstrates unusual double-channel regime with independent channel’s conductance quantization: two side gates can drive the conductance of the separate channels independently. A possible electrostatic mechanism of the double-channel structure formation inside a single constriction is connected with the lateral redistribution of the low-mobility X-valley electrons contained in superlattice layers, resulting in the emergence of the potential barrier in the middle of quantum point contact, separating the conducting electrons into two channels, symmetrically shifted towards the lithographical trenches, defining the nanostructure geometry.

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