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In this work, we theoretically investigate the material and transport properties of strained chevron graphene nanoribbons (CGNRs) which can be easily synthesized by the bottom-up fabrication technology. Because of the unique atomic structures, the energy and pressure of the CGNRs vary asymmetrically along compressive and tensile strains. Under the two strain directions, the CGNRs' bandgaps and carrier effective masses in the conduction band minimum and the valence band maximum are all reduced. The transport properties are promoted accordingly, except some negative differential conductance behaviors caused by energy state localizations. When the tensile strains exceed a criterion value, the C–C bonds in the inner sides of the CGNR corners will be broken in sequence. Meanwhile, the CGNRs can restore their initial unstrained states rapidly when the strains are removed. However, if the broken bonds are saturated by foreign atoms, such as H, a novel kind of stable carbon structure will be obtained. The investigations suggest possible applications of strain engineered CGNRs in transport devices. [ABSTRACT FROM AUTHOR]

Si/Ge core/shell nanowires have been demonstrated to be a promising candidate for the next-generation transistor channel. The tunable electron and hole transport paths improve their mobilities significantly. Here, we comparatively investigate the electronic properties of the Si-core-Ge-shell and Ge-core-Si-shell nanowires and their pure material counterparts using the first-principles method. The effects of core/shell ratio, atom number, and cross-sectional shape are studied. The Si-core-Ge-shell nanowires show excellent transport path separation and small carrier effective mass properties when the core/shell ratios exceed 0.5. For smaller ratios, the energies of the off-&#915 valleys in the Ge shells are lowered and become the conduction band minimum (CBM) because of the intrinsic strains along the radial direction, enlarging the electron effective masses significantly. To restrain this effect, the uniaxial strain engineering is adopted and the best performance is exhibited when 2%–3% tensile strains are applied. In the Ge-core-Si-shell nanowires, both electrons and holes are easily confined to the core region. Compared with the Si-core-Ge-shell nanowires, their energy gaps and electron effective masses are smaller and larger, indicating poor transportability. The above discoveries are further validated by changing the cross-sectional shapes of the nanowires and device performance simulations, confirming that the Si-core-Ge-shell nanowires can outperform their pure material counterparts in high-speed transistor designs. [ABSTRACT FROM AUTHOR]

In this paper, segmented edge saturation (SES) is proposed as a novel method to design high-performance tunnel FETs (TFETs) using smooth graphene nanoribbon (GNR). When the edges of a smooth GNR are saturated by different elements in its different segments, the energy gaps ( Eg) of these segments can be tuned. Therefore, the tunneling and blocking effects are achieved simultaneously by reducing and enlarging the Eg of GNR in its specific regions. Both high on-to-off current ( I \mathrm{\scriptscriptstyle ON}/I \mathrm{\scriptscriptstyle OFF}) ratio and large I \mathrm{\scriptscriptstyle ON} are obtained. Simulation results show that the \mathrm I \mathrm{\scriptscriptstyle OFF} of the SES GNR TFET is below 1 \times 10^-4 ~\mu \textA/\mu \textm and the I{ \mathrm{\scriptscriptstyle ON}} reaches 2000 \mu \textA/\mu \textm at 0.4-V supply voltage. Detailed transport mechanisms of this TFET are investigated in comparisons with its uniform saturation counterparts. Dynamic performance and scaling ability analyzes are also carried out. The largest intrinsic delay and switching energy are only 0.17 ps and 0.09 fJ/ \mu \textm . Meanwhile, it can maintain high I{ \mathrm{\scriptscriptstyle ON}}/I \mathrm{\scriptscriptstyle OFF} ratios when the channel length is scaled down to several nanometers. The discussions on GNR edge roughness suggest that the roughness should be avoided for better I \mathrm{\scriptscriptstyle ON} behaviors. The good performance of the TFET highlights the capabilities of SES in the developments of GNR tunnel devices. [ABSTRACT FROM AUTHOR]

A detailed simulation study of the graphene antidot nanoribbon (GANR) and its corresponding MOSFET characteristics is shown in this paper. The research uncovers that the GANR's energy gap ( E g ) is continuously tunable by its topography parameters, such as the ribbon's width, the antidot density and the antidot size. At the same ribbon width, the E g of GANR can be tuned flexibly, while it is only a fixed value in GNR. Owing to these flexible E g regulations, device applications based on GANRs could be more widely used. Furthermore, brief compact descriptions are extracted between GANR's band gap and MOSFET's device characteristics. Using E g as a bridge, the relations between the structure characteristics and transport properties of GANR MOSFETs are constructed directly. The results reveal that the antidot nanoribbon structure is a good candidate for MOSFET applications. In the calculation, an elaborate ab initio-based study framework from band structure to device performance is adopted. Using the maximally localized Wannier functions (MLWF) method, the impacts on band structures, which are induced by crystal optimizations, are reserved into the TB Hamiltonian without any parameter revisions. This method overcomes the gap between nano-scale carbon structures' material characteristics and their device applications. [ABSTRACT FROM AUTHOR]