2D Materials Nanoelectronics: New Concepts, Fabrication, Characterization From Microwaves up to Optical Spectrum

Aldrigo

Physica Rapid Research Ltrs

et al. 2021

Self Cite

In memoriam of Prof. Dan Dascalu IntroductionHafnium oxide (HfO 2 ) is the dielectric commonly used in fieldeffect transistors (FETs) fabricated in complementary metal oxide semiconductor (CMOS) technologies and, as such, retrieved in any very large-scale integrated (VLSI) circuits. Examples of such circuits include microprocessors or complex analog integrated circuits found in daily applications, for instance, in computers, smartphones, laptops, or incorporated in cars, airplanes, or medical equipments. Since the discovery of HfO 2 as a dielectric for modern integrated circuits, increasing its permittivity was a leading research issue in itself because higher permittivity values allow decreasing the effective oxide thickness (EOT), and so the leakage current; this is especially important when billions of Si FETs are integrated on a single chip. The solution found to boost the permittivity of HfO 2 is represented by structural phase transformations. [1] HfO 2 has its lowest electrical permittivity (ε r % 18) in its stable phase, which is the monoclinic phase. Higher permittivity values, of ε r % 27 in the cubic phase and ε r % 70 in the tetragonal phase, are achieved, nonetheless, in phases that are stable only at very high temperatures, exceeding 1700 C. The decrease in these temperatures is possible, however, by HfO 2 doping. Thus, the cubic and the tetragonal phases were first obtained at lower temperatures via Y doping [1] and, respectively, Si doping, [2] whereas a stable HfO 2 tetragonal phase at nearly room temperature was observed by growing HfO 2 via atomic layer deposition (ALD) and doping it with ZrO 2 . [3,4] As described in the recent review, [5] the stabilization of these phases is determined by the concentration of dopants, the annealing temperature, and the growing methods.These initial investigations focused on increasing the permittivity of HfO 2 lead eventually to the discovery of the orthorhombic phase of HfO 2 , which was associated with HfO 2 ferroelectricity. [6,7] This phase is obtained under different growth conditions in the presence of dopants, including those mentioned earlier, and requires strict control of dopant concentration, temperature, and mechanical strain. The most used orthorhombic HfO 2 -based ferroelectric, named further as Hf ZrO, is doped with Zr and is usually grown at the wafer level, up to 300 mm, using ALD. It thus benefits from the state-of-the-art CMOS technology. More recently, using Zr-doping and pulsed laser deposition (PLD), another rhombohedral phase of HfO 2 was discovered to be also ferroelectric. [7] The rhombohedral or orthorhombic Hf ZrO are ferroelectrics with similar electric performances; the origin of stable ferroelectricity in both cases being due to the induced strain between the top and/or down substrates sandwiching Hf ZrO. [8] Doping or strain application modifies the atomic structure of a material and can induce a phase transition, in particular can induce ferroelectricity in HfO 2 . Similarly, HfO 2 can transform into a weak magnetic material [9...

Section: Atomically Thin Ferroelectricsmentioning

confidence: 99%

HfO₂‐Based Ferroelectrics Applications in Nanoelectronics

Aldrigo

Physica Rapid Research Ltrs

et al. 2021

Self Cite

“…The intrinsic dilemma between the miniaturization of semiconductor devices based on the currently prevalent silicon (Si) material and the quantum interference induced by the extremely small size calls for brand-new micro-nanoscale materials. [1][2][3][4][5][6] Since the 1980s, the significant role of dimensionality has been recognized apart from the bulk phase, inspiring the swift development of low-dimensional materials (0D, 1D, 2D). [7][8][9][10] The realm of 0D quantum dots, [11][12][13][14] 1D nanowire, [15][16][17][18][19] nanotube, [20][21][22][23][24] etc., has become hot research spots in succession.…”

Section: Introductionmentioning

confidence: 99%

Toward Wafer‐Scale Production of 2D Transition Metal Chalcogenides

Wang

Yang

2021

Adv Elect Materials

When the timeline reached 2004, graphene, the single layer of graphite, was discovered through a scotch-tape exfoliation method and was found to have ultrahigh mobility. [25][26][27] Various 2D materials such as transition metal chalcogenides (TMCs), [28][29][30] boron nitrides (BNs), [31,32] black phosphorus, [33,34] and some new materials including Si, [35] Te, [36] and black arsenic-phosphorus [37] were subsequently synthesized, enabling the fabrication of numerous novel devices. The field of 2D materials is now making strong voice, which is no longer ignored by the scientific and technological community. [38][39][40] Among the various 2D materials, the TMCs constituted by the transition metal elements (M) and the chalcogen elements (X) are a large family. M can range from group 4B to group 10 in the periodic table, while X is S, Se, or Te. [41][42][43][44][45][46][47] Figure 1a exhibits the binary TMCs that have already been explored. This variation of composition of elements transfers to a wide range of properties ranging from insulators (e.g., HfS 2 ), [48,49] semiconductors (e.g., MoS 2 , WS 2 ), [50,51] semimetals (e.g., MoTe 2 , TiSe 2 ), [52,53] to metals (e.g., NbSe 2 , VS 2 ). [54][55][56] Furthermore, TMCs can form alloys in the formula such as WSe 2−x S x , with composition-tunable properties. [57][58][59] Unlike semimetallic graphene, semiconducting TMCs usually possess a bandgap. For example, MoS 2 exhibits a bandgap, transitioning from indirect bandgap to direct bandgap when it thins from bulk phase to monolayer (Figure 1b), boosting the photoluminescence (PL) efficiency. [51,[60][61][62] Additionally, inversion symmetry breaking and large spin-orbit interaction, resulting in two energetic degenerate but inequivalent valleys in the band structure of a TMC (Figure 1c), may lead to breakthroughs in valleytronics and spintronics. [63][64][65][66][67][68][69][70] A few TMCs (e.g., NbSe 2 , TaS 2 , VSe 2 ) have shown superconductivity, [71,72] charge density wave [73,74] and Mott transition (transition from metal to nonmetal). [75,76] In addition, some novel TMCs such as Fe 3 GeTe 2 display intrinsic magnetism with gate-tunable Curie points. [66,77] Semimetallic TMCs like WTe 2 show topological structures in the energy band, enabling the study on topological physics. [78,79] The rich intrinsic properties and superior tunability of TMCs hold great promise for all kinds of technologically important applications in electronics, optoelectronics, spintronics, valleytronics, etc. (Figure 1d). [51,[80][81][82][83][84][85][86][87][88][89][90][91] Due to numerous unique properties of 2D TMCs, devices such as transistors, photodetectors (PDs), and photodiodes based on 2D TMCs have been actively pursued. The ultimate destination of the miniaturization of the electronic devices will 2D transition metal chalcogenides (TMCs) have attracted tremendous interest from both the scientific and technological communities due to their variety of properties and superior tunability through layer number, composition, and inter...

“…The experimental study of the optical properties of graphene began in 2004 with the work of Novoselov et al [1,2], which was preceded by some theoretical studies. As long as graphite has been studied, so has monolayer graphene.…”

Section: Introductionmentioning

confidence: 99%

Properties of Bilayer Graphene Quantum Dots for Integrated Optics: An Ab Initio Study

2020

Due to their bandgap engineering capabilities for optoelectronics applications, the study of nano-graphene has been a topic of interest to researchers in recent years. Using a first-principles study based on density functional theory (DFT) and thermal DFT, we investigated the electronic structures and optical properties of bilayer graphene quantum dots (GQDs). The dielectric tensors, absorption spectra, and the refractive indexes of the bilayer GQDs were obtained for both in-plane and out-of-plane polarization. In addition, we calculated the absorption spectra via time-dependent DFT (TD-DFT) in the linear response regime. The TDDFT results show that a blue shift occurs in the absorption spectrum, which is consistent with the experimental results. In this investigation, we consider triangular and hexagonal GQDs of various sizes with zigzag and armchair edges. Our simulations show that unlike monolayer GQDs, for which light absorption for out-of-plane polarization occurs in the ultraviolet wavelength range of 85–250 nm, the out-of-plane polarization light absorption peaks in the bilayer GQDs appear in the near-infrared range of 500–1600 nm, similar to those in bilayer graphene sheets. The out-of-plane polarization light absorption peaks in the near-infrared range make bilayer GQDs suitable for integrated optics and optical communication applications.