Fabrication of highly ordered vertical GaAs nanowires by inductively coupled plasma etching and their modal analysis

Highly ordered vertical gallium arsenide (GaAs) nanowires are fabricated by dry etching using various metal mask combinations. A great control on length, diameter, pitch and facet tapering of the nanowires is achieved. Diameters ranging from 30 nm to 250 nm with pitch ranging from 200 nm to 1100 nm and length up to 2 μm are fabricated using this process. The highest diameter to pitch ratio is ∼68%. The reflection measurements are performed on the samples and the diameter dependent strong absorption peaks due to optical modal excitations are observed from the refection measurements. Finite difference time domain (FDTD) analysis is used to validate the measurements and the absorption characteristics are understood. The modal analysis is also performed from the same simulations. The hybrid cylindrical waveguide modes as the function of nanowires diameter are identified to be linear. Also the near field coupling between the nanowires is absent even at the small pitches.