The Electronic Properties Of Silicene And Transport Properties Of Metallic Wires: A First Principle Study

According to the Moore’s law, the size scaling in digital logic has enabled thecomplexity of integrated circuits to double every12to18months, leading to significantimprovements in performance and diminutions in price per transistor, and also theincrements in the number of challenge.First, one of the most important parts in integrated circuits is investigated, themetal-oxide-semiconductor field effect transistor (FET). For high-speed applications, FETsshould respond quickly to variations in the voltage applied between the gate and source; thisrequires short gates and fast carriers in the channel. Unfortunately, the FETs with short gatesfrequently suffer from short channel effects. Scaling theory predicts that a FET with a thinbarrier and a thin channel region will be robust against short-channel effects down to veryshort gate lengths. The possibility of having channels that are just one atomic layer thick isperhaps the most attractive feature of silicene for use in transistors.Silicene, the Si analogue of graphene, is a promising material for electronic applicationswhile its linear band structures in Fermi energy suggest the high carrier mobility. Moreover,it supplies an ideal interface with the existing Si devices and takes advantage of tractablematerial technology. Thus, the possibility of silicene as the channel in FETs is studied. Theelectronic structures and band gaps of silicene adsorbed with halogen elements are studiedusing the density functional theory based screened exchange local density approximationmethod. It is found that the structural stability increases for silicene with surfacefunctionaliztion. Moreover, the band gaps of silicene adsorbed with F, Cl, Br and I have anonmonotonic change as the periodic number of the halogen elements increases. This isattributed to the transfer of contributions to band gaps from Si–Si bonding to Si–halogenbonding. In addition, the band gap values of silicene with F and I functionalization are closeto those of GaAs and bulk Si, thus those are potential to be used as the channels in FETs.However, the high carrier mobility of silicene is broken seriously by the surfacefunctionalization. Our calculations show that opening a sizeable band gap of silicene withoutdegrading its carrier mobility can be realized by silicene/substrate hybrid structures withnoncovalent interface interactions. Several possible two-dimensional semiconductingsubstrates are selected to find the factors those control the magnitude of band gap. It is found that the more notable charge redistribution in two sublattices of silicene and thus a largerband gap are characterized by a smaller interlayer distance. Thus, the opened band gap inhybrid structures with SiH/π interaction has reached the technique requirement ofroom-temperature operation in FETs. Recently, it was reported that the Si single layer withhoneycomb structure grew on the MoS2substrate. Thus, the geometric and electronicproperties of silicene paired on MoS2substrate are studied systematically by using densityfunctional theory with van der Waals correction. It is found that the nearly linear banddispersion can be preserved in the heterobilayers due to the weak interface interactions.Meanwhile, the band gap is opened because of the sublattice symmetry broken by theintrinsic interface dipole. Moreover, the band gap values could be effectively modulatedunder an external electric field. Therefore, a way is paved for the silicene/MoS2heterobilayers as the candidate materials for logic circuits and photonic devices.Finally, we investigate the interconnect that connects the parts in integrated circuits. Inkeeping with the Moore’s law, the miniaturization of chip dimensions also creates the needto downscale interconnects. The bulk conductivity of presently used Cu is superior to nearlyall conventional metals (except Ag), while the electrical conductivity is one of essentialrequirements for interconnects. However, as the size approaches the electron mean free path,the electrical conductivity deviates downward from their bulk value seriously induced bysurface and grain boundary scatterings. Thus, we study the structural and quantum transportproperties of Al and Cu nanowires with diameters up to3.6nm using density functionaltheory combined with the Landauer formalism. Contrary to the classical electronic behavior,the conductance of Al wires is larger than that of Cu. This is mainly attributed to the largercontribution of conductance channels from Al-3p, which is determined by the chemicalnature. Meanwhile, the stronger axial contraction of Al wires plays a minor role toconductance. This makes Al wires possible candidate of interconnects in integrated circuits.