Fabrication, Structure and Hydrogen-gas-sensing Properties of Multiple Networked GaN Nanostructure Gas Sensors

The controlled synthesis of nanostructures with different shapes and morphologies has attracted considerable interest because the sensing properties of nanostructures depend on their structure, shape, phase, size, and size distribution, as well as their composition. This paper compares the responses of GaN nanostructures with different morphologies to hydrogen. The underlying mechanism for the hydrogen gas sensing of the multiple networked GaN nanowire sensor can be explained based on the well-established surface depletion model. On the other hand, the difference between two different samples, the GaN nanostructure sample synthesized at 1,100 ◦C and that synthesized at 1,000 ◦C, could be explained as follows: The major process behind the interaction between the nanostructures and hydrogen is the chemisorption of the dissociated hydrogen on the GaN surface. The chemisorption creates an electron accumulation layer on the GaN surface that enhances its electrical conductance. The GaN nanostructure sample synthesized at 1,100 ◦C with a higher ammonia flow rate showed a higher response to H2 gas than that synthesized at 1,000 ◦C with a lower ammonia flow rate, which might be attributed to the higher surface-to-volume ratio of the former.