A catalyst-free method for growing self-assembled GaN wires on c-plane sapphire substrates by metal-organic vapour phase epitaxy has been developed using a commercial Close Coupled Showerhead reactor. This approach, based on in situ deposition of a thin SiNx layer (around 2 nm), enables epitaxial growth of c-oriented wires with 200–1500 nm diameters and a large length/diameter ratio (>100) on c-plane sapphire substrate. The detailed study of the growth mechanisms shows that a combination of key parameters is necessary to promote the vertical growth, in particular the duration of the SiNx deposition prior to the wire growth, the GaN seed nucleation time and a high Si-dopant concentration. Such GaN n-doped wires exhibit UV-light emission centred at about 350 nm and a weak yellow band (around 550 nm) at low temperature.

For practical applications, the advantage of this vapour phase technique comes from the very simple surface preparation, which does not require any surface patterning for selective growth and metal catalyst. A fast growth rate of several tens of micrometres per hour can be achieved with a very good uniformity in length over a large area.

The current activities of the researchers involved in this study are mainly focused on understanding the basic physical properties of the wires in terms of the structure/growth mechanisms and optical features. Such wires make interesting templates for growing InGaN/GaN multiple quantum-well radial heterostructures for light emission on non-polar surfaces (the edges of the wires). The control of the emission wavelength and efficiency of these heterostructures are under development as well as doping issues.

The researchers presented their work in the journal Nanotechnology.