Theoretical investigations of Ge nanowires grown along the [110] and [111] directions

An ab initio study of Ge nanowires (GeNWs) oriented along [110] and [111] directions is performed for H-passivated and non-passivated wires with diameters up to 3.5 nm. GeNWs grown in the [110] direction present a direct energy gap and in the [111] direction the energy gap is indirect, even for small diameters. The highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gap scales with diameter, d, as proportional to d(-0.9) and d(-1.1) for the [110] and [111] growth directions, respectively. Consequently for the same diameter GeNWs grown in the [110] direction present a smaller gap than nanowires grown in the [111] direction.