Edge functionalized germanene nanoribbons: impact on electronic and magnetic properties

Abstract

Germanene exhibits extremely high mobility, massless fermion behavior, and strong spin–orbit coupling drawing tremendous interest for high performance devices. It has a buckled two-dimensional structure, but not the intrinsic energy band gap and structural stability required for logic and switching devices. Application of a perpendicular electric field, surface adsorption, confinement of an armchair nanoribbon structure and edge functionalization are methods used to open a band gap. Edge functionalization of armchair germanene nanoribbons (AGeNRs) has the potential to achieve a range of band gaps. The edge atoms of AGeNRs are passivated with hydrogen (–H and –2H) or halogen (–F, –Cl, –OH, –2F, –2Cl) atoms. Using density functional theory calculations, we found that edge functionalized AGeNRs had band gaps as small as 0.012 eV when functionalized by –2H and as high as 0.84 eV with –2F. Formation energy studies revealed that AGeNRs produced a more stable structure under fluorine functionalization. Simulation results suggest that the electronic structure of germanene is similar to graphene and silicene. A spin-polarized density functional theory (DFT) study of electronic and magnetic properties of pristine, chemically functionalized and doped AGeNRs and zigzag nanoribbons (ZGeNRs) was performed. Formation energy studies revealed that the Ge atoms at the edge of the ribbon prefer to be replaced by impurity atoms. Doping can change the semiconducting behaviour of AGeNRs to metal behaviour due to the half-filled band making it useful for negative differential resistance (NDR) devices. In the case of ZGeNRs, single N or B doping transformed them from anti-ferromagnetic (AFM) semiconducting to ferromagnetic (FM) semiconducting or half-metal. These magnetic and electronic properties make edge functionalized doped AGeNRs and ZGeNRs promising for use in field effect transistors (FETs) and spintronics. Finally, energy band gap tuning of AGeNRs and ZGeNRs using edge functionalization may open a new route to integrate germanene in logic and high performance switching devices.