Synthesis of vertically-aligned GaAs nanowires on GaAs/(111)Si hetero-substrates by metalorganic vapour phase epitaxy

We report on the Au-catalysed synthesis of GaAs nanowires on hetero-structured GaAs/(111)Si substrates by metalorganic vapour phase epitaxy. It is demonstrated that the deposition of a 40-50 nm thin GaAs epilayer onto Si guarantees a high percentage of straight and vertically-aligned GaAs nanowires. GaAs epilayers were grown at 400 degrees C and subsequently annealed at 700 degrees C. Growth experiments performed on 4 degrees-miscut and exactly-oriented (111)Si substrates show that a higher yield (close to 90%) of vertical nanowires is obtained using miscut substrates, an effect ascribed to the smoother surface morphology of GaAs epilayers on these substrates. Comparison between the cross-sectional shape of nanowires grown on GaAs/(111)Si hetero-substrates and those on (111)A-GaAs and (111)B-GaAs substrates demonstrates that both GaAs epilayers and over-grown nanowires are (111)B-oriented.