Nanowires made from semiconducting materials are widely investigated for electronic devices because compared to their bulk counterparts low-dimensional nanostructures offer novel properties. However, the efficient large-scale fabrication of nanowires is important for practical applications. Researchers from Tsinghua University in Beijing1 now demonstrate that electrospinning is such promising high-yield fabrication method.

In electrospinning, an electric voltage is applied to create strong electrostatic repulsion at the surface of a liquid. This can lead to the expulsion of droplets from the liquid, or even very thin fibers if the liquid’s viscosity is sufficiently low.

Fig. 1: Schematic of optotelectronic devices based on electrospun gallium nitride nanofibers.

In their electrospinning approach, the researchers used a precursor made from a polymer and gallium nitrate mixture. The composite fibers were then heated at high temperatures to evaporate all organic components, thereby forming gallium oxide nanowires. Further heat treatment in an ammonium atmosphere then converted the gallium oxide nanowires into gallium nitride nanowires. The resulting nanowires were only about 40 nm in diameter (Fig. 1).

Importantly, this process requires no catalysts and no templates. “Our solution-based approach is low-cost and high-efficiency,” says team leader Pan Wei. “It can be extended to the fabrication of other nitride semiconductors such as indium nitride and indium gallium nitride.”

The researchers found that the nanowire conductance was strongly dependent on illumination with ultraviolet light, with a difference of more than two orders of magnitude between the illuminated and the dark states.

Furthermore, the photosensitivity of the electrospun nanowires was much greater than that of single-crystalline gallium nitride nanowires produced by other methods. This was attributed to the polycrystalline nature of the wires as well as a rougher surface that led to a larger surface-to-volume ratio. Such beneficial properties make these electrospun nanowires ideal candidates for optoelectronic applications.

In a further demonstration of the flexibility of this approach, the researchers also introduced manganese into the fiber precursor and obtained gallium nitride nanowires doped with manganese. As was expected from the properties of the corresponding bulk material, the resulting nanowires were ferromagnetic.

“These results provide a new method for the low-cost growth of low-dimensional semiconductor nitride nanostructures,” says Wei.