Scanning electron micrographs obtained for MQW-nanotubes uncomplete etching of the GaN core (a) or for complete etching (b). The 70 nm thin nanotube is made of 10 GaN/InGaN quantum wells. (c) Schematic illustration of the etching mechanism leading to the formation of the nanotubes.
Several groups have already reported the fabrication of nanotubes, but such structures exhibit usually poor light emission performances. Indeed, the surface states and defects favor the non-radiative recombination processes that quench light emission. To overcome this problem, we have developed a novel type of nanotubes with walls only composed of multiple quantum wells (MQWs), acting as the active region for light emission. Quantum wells are well known for their remarkable light emission properties due to quantum confinement effects and are very widely used in light emitting diodes and laser diodes.
To successfully produce such MQW-nanotubes, GaN wires coated with a core-shell GaN/InAlN MQW heterostructure have first been synthesized by metal-organic vapor-phase epitaxy (MOVPE). These wires have next been annealed in a mixed H2/NH3 atmosphere. This annealing only etches the inner GaN wire, thus producing nanotubes only composed of MQWs. We have demonstrated by ToF-SIMS measurements that the tube walls are actually composed of the GaN/InAlN heterostructure, which shows that the annealing does not degrade the quantum wells. Such advanced MQW-nanotubes display excellent light emission properties in the UV range (around 330 nm) at room temperature. The simplicity of this fabrication method opens attractive routes for the development of novel nanotube-based devices, ranging from UV light emitters to chemical and biological sensors.
This work was performed in close collaboration with the Professor Nicolas Grandjean’s group at EPFL (Ecole Polytechnique Fédéral de Lausanne - Switzerland). This study has been supported by the program Franco-Swiss “Partenariats Hubert Curien (PHC) Germaine de Staël” and the Labex LANEF.
Last update : 05/24 2017 (1252)