ABSTRACT
To overcome the scaling restriction on silicon-based field-effect transistors (FETs), two-dimensional (2D) transition metal dichalcogenides (TMDs) have been strongly proposed as alternative materials. To explore the device performance limit of TMD-based FETs, in this work, the ab initio quantum transport approach is utilized to study the transport properties of monolayer VTe2/WTe2 heterojunction-based FETs possessing double gates (DGs) with a 5 nm gate length (Lg). Our theoretical simulations demonstrate that the DG-cold-source VTe2/WTe2 FETs with a 5 nm Lg and 2 or 3 nm proper underlap (UL) meet the basic requirements of the on-state current (Ion), power dissipation (PDP), and delay time (τ) for the 2028 needs of the International Technology Roadmap for Semiconductor (ITRS) 2013, which ensures their high-performance and low-power-dissipation device applications. Moreover, the DG-cold-source VTe2/WTe2-based FETs with a 3 nm Lg and 2 or 3 nm UL meet the high-performance requirements of Ion, τ, and PDP for the 2028 needs of ITRS 2013. Additionally, by further considering the negative capacitance technology in devices, the parameters τ, Ion, and PDP of the VTe2/WTe2-based FETs with a 1 nm Lg and 3 nm UL meet well with the 2028 needs for ITRS 2013 towards high-performance device applications. Our theoretical results uncover that the 2D DG-cold-source VTe2/WTe2 FETs can be used as a new kind of promising material candidate to drive the scaling of Moore's law down to 1 nm.
ABSTRACT
Low-dimensional materials have been proposed as alternatives to silicon-based field-effect transistor (FET) channel materials in order to overcome the scaling limitation. In the present research, gate-all-around (GAA) Sb2Se3 nanowire FETs were simulated using the ab initio quantum transport method. The gate-length (Lg, Lg = 5 nm) GAA Sb2Se3 FETs with an underlap (UL, UL = 2, 3 nm) could satisfy the on-state current (Ion) and delay time (τ) of the 2028 requirements for high performance (HP) applications of the International Technology Roadmap for Semiconductors (ITRS) 2013. It is interesting that the Lg = 3 nm GAA Sb2Se3 FETs with a UL = 3 nm can meet the Ion, power dissipation (PDP), and τ of the 2028 requirements of ITRS 2013 for HP applications. Therefore, GAA Sb2Se3 FETs can be a potential candidate scaling Moore's law downward to 3 nm.
ABSTRACT
Tremendous attention has been paid to vertically stacked heterostructures owing to their tunable electronic structures and outstanding optical properties. In this work, we explore the structural, electronic and optical properties of vertically stacked GaN/WX2 (X = S, Se, Te) heterostructures using density functional theory. We find that these stacking heterostructures are all semiconductors with direct band gaps of 1.473 eV (GaN/WTe2), 2.102 eV (GaN/WSe2) and 1.993 eV (GaN/WS2). Interestingly, the GaN/WS2 heterostructure exhibits a type-II band alignment, while the other two stackings of GaN/WSe2 and GaN/WTe2 heterostructures have type-I band alignment. The optical absorption of GaN/WX2 heterostructures is very efficient in the visible light spectrum. Our results suggest that GaN/WX2 heterostructures are promising candidates for photocatalytic water splitting and photoelectronic devices in visible light.
ABSTRACT
A hybrid structure of carbon nanotubes and graphene nanoribbons was predicted and synthesized (Y. Li et al., Nat. Nanotechnol., 2012, 7, 394-400; P. Lou, J. Phys. Chem. C, 2014, 118, 4475-4482). Herein, using the non-equilibrium Green's function (NEGF) combined with density functional theory (DFT), the thermal spin transport properties and the figure of merit (a material constant proportional to the efficiency of a thermoelectric couple made with the material) of a composite of single-walled carbon nanotubes and zigzag-edge graphene nanoribbons, labeled (6,6)SWCNT/n-ZGNR, are investigated for n = 1, 2, 3, and 8. The results manifest that spin-dependent currents with opposite flow directions were generated when a temperature gradient was applied between two electrodes, indicating the occurrence of the spin-dependent Seebeck effect (SDSE). Remarkably, when n = 3, the charge current is equal to zero, meaning that a perfect SDSE is observed. Moreover, a pure spin-dependent Seebeck diode (SDSD) effect can be observed. Finally, we notice that the device presents an n-type characteristic when n = 1, while the device has a p-type feature when n = 2. In particular, the spin-up thermopower is equal to the spin-down thermopower when n = 3; as a consequence, the charge thermopower is equal to zero, further demonstrating that a perfect SDSE is generated. These discoveries indicate that the (6,6)SWCNT/n-ZGNR is a promising candidate for spin caloritronics devices.
ABSTRACT
Metal-free magnetism and spin caloritronics are at the forefront of condensed-matter physics. Here, the electronic structures and thermal spin-dependent transport properties of armchair graphene nanoribbons (N-AGNRs), where N is the ribbon width (N = 5-23), are systematically studied. The results show that the indirect band gaps exhibit not only oscillatory behavior but also periodic characteristics with E 3p > E3p+1 > E3p+2 (E 3p , E3p+1 and E3p+2 are the band gaps energy) for a certain integer p, with increasing AGNR width. The magnetic ground states are ferromagnetic (FM) with a Curie temperatures (T C ) above room temperature. Furthermore, the spin-up and spin-down currents with opposite directions, generated by a temperature gradient, are almost symmetrical, indicating the appearance of the perfect spin-dependent Seebeck effect (SDSE). Moreover, thermally driven spin currents through the nanodevices induced the spin-Seebeck diode (SSD) effect. Our calculation results indicated that AGNRs can be applied in thermal spin nanodevices.
