Spin transport in substitutionally doped graphene nanoribbons

Abstract

Recent fabrication of graphene nanoribbon (GNR) based field effect transistor (FET) has made all-carbon electronic device a reality. GNR can be metal or semiconductor with the variation of its edge orientation and width and is expected a promising material for quantum electronic devices in the future. In addition, magnetic properties which are difficult to be exploited in conventional semiconductor devices can be easily manipulated in GNRs via artificially introducing defects or doping. This great advantage together with the long coherence distance for both charge and spin in these structures has made GNR a very intriguing material for spintronics as well as electronics. In particular, zigzag GNR is one of the most attractive systems due to its peculiar edge states, which are showing ample potential in spintronic applications. Different methods have been proposed to developing useful properties of ZGNRs with the help of defects, gate voltage, chemical adsorption, doping, etc.We report ab initio simulations of spin transport in zigzag GNRs of different width when one carbon in various distances from the edge is substituted by an atom of other elements such as 0, AI, B, Be, and P etc., as illustrated in Fig.l, within the framework of density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) method implemented in Atomistic TooKits. In some cases, this system shows unique properties different from those previously reported. For a perfect semiconductor 4-ZGNR, the transmission spectrum shows a gap near the Fermi energy with a narrow two-channel peak at the lower boundary of the gap. When a C atom at edge is substituted by a Be atom, it remains in similar profile with reduced amplitudes for spin-down electrons, but for spin-up electrons the transmission peak disappears and an extra narrow side gap appears at the upper boundary of the main gap as shown in Fig.2. The contrast effects of the doping on the spin-up and spin down energy bands and transmissions result in strong spin dependent charge transport.Negative differential conductance may appear only for spin-down electrons in the considered bias range as shown in Fig.3.