Nano Research & Applications

Description

A two-dimensional ternary tetrahexagonal BCN monolayer (th-BCN) is designed by applying Stone-Wales transformation to its pentagonal counterpart (p-BCN). Using first-principles calculations, we examine the dynamical, mechanical, thermal, and environment stability of th-BCN. The monolayer exhibits superior anisotropic electronic and optical properties compared to its counterparts (the domains of C and BN in the tetrahexagonal network and p-BCN). Direct band gap of 3.05 eV and excellent band edge alignment with the oxidation and reduction reactions of water heralds the use of th-BCN in photocatalytic water splitting. The band gap energy and band edge positions can be further adjusted by strain. The anisotropic high carrier mobility of th-BCN improves fast carrier separation and low recombination rate. The electronic transport direction can be easily controlled by strain engineering. For instance, one can rotate the preferred transport direction of hole by 90° with a very small uniaxial strain. Many-body effects beyond DFT reveal that the monolayer has strong light-harvesting capability (105cm−1) in the visible-ultraviolet region and exhibits strong excitonic effects with large excitonic binding energy of 0.98 eV. All these appealing properties make th-BCN a promising and tunable anisotropic 2D material for nanoelectronic and optoelectronic applications. Plasma-based technology can be used to fabricate nanoelectrodes and ultra-thin oxide films for nanoelectronics. Plasma technologies can also be used for material processing in nanoelectronics and synthesis of semiconductor nanocrystals for nanoelectronics and luminescence applications. On the other hand, plasma chemical etching of silicon has been widely used in nanoelectronics. This chapter focuses on the use of plasma-based technology in nanoelectronics.

Material Processing in Nanoelectronics

 Various kinds of plasma-based technology have been widely used, such as plasma patterning, plasma-enhanced chemical vapor deposition, plasma-assisted inkjet printing, plasma antennas, plasma switches, etc. The great success of graphene has encouraged tremendous interest in searching for new two-dimensional (2D) carbon allotropes. Based on first-principles calculations, we proposed new 2D carbon allotropes obtained from the assembly of fenestrane molecule unit, named as four-penta-graphenes. The fPG monolayers are energetically more favorable than pentagraphene and show excellent dynamical, thermal, and mechanical stability. They exhibit exotic mechanical properties including anisotropic in-plane stiffness and auxetic behavior with sign-tunable Poisson's ratio. Their electronic properties are diverse, ranging from narrow band gap semiconductors to metal. The electronic band gap and band edge positions of the fPG semiconductors can be flexibly modulated by strain engineering. Indirect-to-direct band gap and semiconductor-to-metal transitions can be achieved by applying compressive and tensile strains, respectively. High mobility and anisotropic effective mass of carriers make these materials promising for nanoelectronics. Using many-body GW0+BSE approximations, we reveal that the fPG semiconductors exhibit strong excitonic effects with distinct optical absorption peaks in the visible range. These remarkable optical properties make them also promising devices for optoelectronics. The real use of nanoelectronics with organic molecules as a replacement of conventional silicon technology faces many challenges because of complications in synthesis and fabrication processes, short stability, junction breakdown, large fabrication costs and environmental influences. The present work aims at proposing a novel alternative by studying the potential of ‘inorganic analogues of the organic components' in molecular electronics. In comparison to their organic counterparts, the higher structural rigidity in inorganic components provides a possible added value in being less susceptible to environmental influences. The structure as well as electronic and transport properties of group three nitride analogues of benzene molecules, namely, the X3N3H6 (X = B, Al and Ga) clusters are analysed and compared with benzene and with melamine, a graphitic carbon nitride (g-C3N4) material. A detailed Density Functional Theory (DFT) investigation is performed for the structural and electronic properties, whereas a combined DFT and non-equilibrium Green's function approach is used for the transport properties. The electron delocalisation with overlapping electronic states, the influence of magnetic fields and favourable quantum chemical properties of Ga3N3H6 clusters make the man outstanding electronic component for future nanoelectronics applications.

 This work gives an overview of the Non-Equilibrium Green function (NEGF) technique in quantum field theory by using Langreth's method. The difference between the diagrammatic Green function (GF) technique for equilibrium and nonequilibrium systems is discussed with respect to Keldysh contour. A short review of the diagrammatic technique for an equilibrium system is presented for various types of interactions that are possible in nanoelectronic devices such as external field, electron-electron interaction, and electron-Boson interaction. Moreover, the Random Phase Approximation (RPA) and Hedin's equation are reviewed with the presence of electron-electron interaction and electron-Boson interaction. Based on Langreth's rules, the Keldysh components of the first two orders of the T-matrix and self-energies, irreducible polarization, and vertex corrections in the presence of the electron-electron and electron-Boson interaction are extracted.

Nanoelectronic Devices

 The RPA and Hedin's equations are formed in Keldysh space in the presence of electron-electron interaction, and electron-Boson interaction. Finally, the application of the NEGF technique to analyze the quantum transport in nanoelectronic devices, i.e., electron transport in metal-insulator-metal tunneling junction, tunnelling resonances system, and nanostructure sensitized photovoltaic device, are discussed. Despite the breathtaking progress already achieved for electronic devices built from 2D materials, they are still far from exploiting their full theoretical performance potential. Many of these problems are due to the lack of suitable insulators which would go along with 2D materials as nicely as SiO2 goes with Si. For instance, amorphous oxides known from Si technologies contain numerous defects which degrade the device performance and stability, and hBN is not suitable for nanoscale devices due to limited dielectric properties. Thus, we suggest that an intensive search of beyond-hBN layered 2D insulators and other crystalline insulators such as CaF2, other fluorides and native oxides is required for the further development of next-generation 2D nanoelectronics. In this work, we perform first-principles density functional theory calculations to study siligraphene/hexagonal boron nitride vdW-heterostructures. Siligraphene has comparable electronic properties to graphene, including the presence of a Dirac-like cone, thus we investigate its potential as a replacement for graphene. We find that, when internal strains induced by the high lattice mismatch between the SiC3 and hBN layers are reduced, a very small and non-tunable gap is induced in a hybrid bilayer heterostructure. However, the picture becomes quite different when structures with higher internal strains are considered. In this scenario, the compressive strain induces a buckling in the SiC3 sheet, resulting in larger band gaps. Additionally, in many configurations, the gaps are found to be quite tunable by the application of external strains or an electrical field. Such tunability is absent in graphene/hBN heterostructures, thus giving SiC3/hBN heterostructures a clear edge. The origin of this gap and its tunability are discussed in terms of the buckling in the SiC3 layer and the interlayer charge transfer. Finally, the optical properties of these heterostructures were also investigated. Strong absorption peaks in both visible and deep UV regions were found, which could be explored for applications in future optoelectronic devices. In this work, we have optimized the device structure to achieve a maximum drain current of Nanoelectronic AlGaN/GaN single-heterojunction high electron mobility transistors by the variations of mole fraction, doping concentration and gate length, using the SILVACO-ATLAS software tool. The drain current increases at higher aluminium mole fraction of AlGaN nano-layer. The drain current increases at higher doping concentration of AlGaN nano-layer. The drain current reduces at higher gate length of HEMTs. The conduction band engineering in terms of quantum wells is investigated in detail by involving the Bose-Einstein expression. The simulation results of this work are supported by the available previous experimental results and analytical modelling. This work will be useful to fabricate the AlGaN/GaN HEMTs experimentally for bioengineering applications.