Credit: © 2006 ACS

Gallium-nitride-based light-emitting devices are widely used in the electronics industry. The physical properties of low-dimensional GaN structures are of particular interest and may hold promise for the construction of novel nanoscale optoelectronic devices. GaN nanowires are currently synthesized by chemical vapour deposition methods that use additional metal catalysts, but these can degrade the crystalline quality of the resulting nanostructures and hence limit their applications.

Now, Stephen Hersee and colleagues1 of the University of New Mexico in the USA have used pulsed metal–organic chemical vapour deposition (MOCVD) and a selective growth mask to make high-quality oriented GaN nanowires without using catalysts. A 30-nm-thick silicon nitride layer was deposited on a GaN film and was then patterned with a hexagonal array of 220-nm-diameter circular openings with a pitch spacing of 500 nm. GaN nanowires with precisely controlled geometry and crystal orientation were then grown using trimethylgallium and ammonia precursors. The nanowires were produced at high growth rates exceeding 2 μm h-1. Furthermore, after growing beyond the mask, the diameter of the nanowires remained constant (to within a few monoatomic layers) along the entire length.

Room-temperature photoluminescence from GaN nanowire arrays was dominated by band-edge emission at approximately 363 nm, with an intensity 200 times greater than bulk GaN thin films. The combination of pulsed MOCVD and dielectric masks for fabricating GaN wires will be a valuable tool for realizing nanoscale optoelectronics based on this material.