Plasma-synthesized Photoluminescent Gallium Nitride Nanocrystals for UV Light*

Gallium nitride (GaN) is a semiconductor material of broad interest for its wide direct band gap, chemical stability, and non-toxicity. Thin-film methods of GaN synthesis are well studied, but synthesis strategies and studies related to spheroidal nanocrystals (NCs) of GaN are lacking. Colloidal or solution-based methods are limited by the synthesis temperature, typically required to be high due to the refractory nature of GaN. We have recently developed a gas-phase, plasma synthesis strategy for freestanding, pure, and size-controlled GaN NCs termed Nonequilibrium Plasma Aerotaxy. It feeds an aerosol of gallium metal carried by argon in addition to nitrogen into a flow-through, low pressure, capacitively-coupled tubular plasma generated by radiofrequency power. By controlling the residence time of the gas and the gallium mass concentration in the reactor, the size of the NCs and therefore their optoelectronic properties can be tuned. More recently, we have measured the photoluminescence quantum yield in the ultraviolet for these NCs and found it to be much higher than any previously reported values for freestanding GaN NCs. The required synthesis conditions, post-processing, and potential for solid-state ultraviolet lighting devices from these NCs will be discussed.