Jan 19, 2010
GaN wires grown spontaneously by vapour phase epitaxy
Researchers at CEA INAC and CNRS Institut Néel have come up with a fast and economical route for fabricating gallium nitride (GaN) wires with metal organic vapour phase epitaxy. The technique would suit the fabrication of UV-light emitters as well as templates for light guiding and also axial and longitudinal nitride heterostructure growths for fabricating wire-based nitride photonic devices.
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.
About the author
The authors worked together in the CEA-CNRS Equipe mixte "Nanophysique et semiconducteurs" in Grenoble. This work has been funded in part by the French government ANR Filemon35 and Carnot Eclairage projects. The main part of the work was performed by PhD student R Koester, who was funded by the EU Marie Curie program "Chemtronics". J S Hwang is a PhD student involved in the optical studies of nanowires. C Durand, D Le Si Dang and J Eymery are respectively members of the Joseph Fourier University, CNRS and CEA organizations.