Opportunities and pitfalls in patterned self-catalyzed GaAs nanowire growth on silicon

Periodic arrays of self-catalyzed GaAs nanowires (NWs) were grown on Si substrates by gas source molecular beam epitaxy (GS-MBE) using patterned oxide templates. The various challenges of the patterning process that result in undesired outcomes are described, such as pattern transfer by wet/dry etching, oxide thickness variations, and native oxide re-growth. Transmission electron microscopy (TEM) results are used to illustrate each case. In particular, we show that a linearly increasing length?radius distribution, analogous to that observed for unpatterned self-catalyzed growth on substrates with thin oxides, may be obtained even when using patterned oxide masks due to an unintended residual layer of oxide, as confirmed by TEM analysis. We explain how a linear length?radius dependence can result from the individual NWs beginning their growth at different times, accompanied by significant radial growth. The spread in obtained NW dimensions was decreased by improving the patterning method.