This work reports the innovative fabrication and detailed electrical characterization of aerogalnite (Aero-GaN), an interconnected network of hollow gallium nitride (GaN) microtetrapods. The material is synthesized by hydride vapor phase epitaxy (HVPE) on a three-dimensional network of ZnO microtetrapods used as a sacrificial template. The resulting Aero-GaN structure consists of an interpenetrating network of hollow GaN microtetrapods and microtubes with wall thicknesses ranging from 40 to 130 nm.

The synthesis process involves two temperature stages. Initially, a low-temperature growth regime (600 °C) promotes nucleation and the formation of an epitaxial GaN layer. This is followed by a high-temperature stage (850 °C) that accelerates GaN film growth while simultaneously inducing the controlled decomposition and removal of the ZnO template in an H₂ + HCl atmosphere [1]. Transmission electron microscopy (TEM) studies reveal that, despite the extensive removal of the sacrificial template, an ultrathin ZnO layer remains on the inner surface of the GaN microtubes. During further growth, this interfacial layer becomes encapsulated, forming spatially discrete buried ZnO layers within the GaN structure [2].

Low-temperature electrical characterization shows that Aero-GaN structures with microtube wall thicknesses of 120–140 nm exhibit a nonuniform dependence of electrical resistance on temperature. Specifically, the resistance decreases with increasing temperature up to approximately 160 K, consistent with typical semiconductor behavior, while a further increase in temperature up to 300 K results in a continuous rise in resistance. This effect is not observed in structures with microtube wall thicknesses below 50 nm.

The electromechanical sensing properties of Aero-GaN embedded in a commercial silicone elastomer (PDMS, Sylgard 184) were also investigated under uniaxial compression. When compressive stresses of up to 5 kg cm⁻² were applied, the electrical resistance increased. This response is attributed both to the intrinsic piezoresistive properties of GaN and to the deformation of the interconnected Aero-GaN microtetrapod network, which alters the effective conductive pathways. This interpretation is supported by the similar increase in resistance observed during uniaxial stretching of the composite material.

Acknowledgements

The authors thank the BMFTR and NARD for funding the ProMoMo project DEHYCONA.

References

[1] I. Tiginyanu; T. Braniste; D. Smazna; M. Deng; F. Schutt; A. Schuchardt; M.A. Stevens-Kalceff; S. Raevschi; U. Schurmann; L. Kienle; N. Pugno; Y. K. Mishra; R. Adelung Nano Energy, 2019, 56, 759-769.

[2] T. Braniste; Z. Fogarassy; A. Kovács; B. Pécz; I. Tiginyanu; In: Sontea, V., Tiginyanu, I., Railean, S. (eds) 7th International Conference on Nanotechnologies and Biomedical Engineering. ICNBME 2025. IFMBE Proceedings, 2026, 134, 104-111.

Dr. Tudor Braniste