Growth And Characterization Of Ga2o3 And Gan Nanostructures For Hydrogen Sensing Application
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Date
2015-08
Authors
ABDULLAH, QAHTAN NOFAN
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Abstract
This project is focusing on the preparation of gallium oxide (Ga2O3) and gallium nitride (GaN) semiconductor nanostructures in simple and low-cost techniques. There were two aims: firstly, to study the growth and characterizations of β-Ga2O3 and GaN nanostructured materials under various growth conditions and secondly, to fabricate hydrogen gas sensors based on β-Ga2O3 and GaN nanomaterials obtained. The characteristics of these nanomaterials subsequently were examined by various tools. For the growth of Ga2O3 nanostructured materials, various morphologies and shapes, such as nanowires (NWs), nanobelts (NBs), and nanosheets (NSHs) have been successfully synthesized directly without any metal catalyst on Si, AlN/Si and ZnO/Si substrates, respectively. In addition, SnO2-coated β-Ga2O3 NBs were grown on Al2O3 substrate, with diameters ranging from 50 up to 200 nm and lengths of NBs up to several of micrometers. On the other hand, for the synthesis of GaN nanostructures, the morphological, structural, and optical characteristics of the grown GaN nanostructures were significantly influenced by the change of growth parameters such as ammoniating time, type of substrate, and flow rate of ammonia gas inside the tube furnace. Based on morphological observations we propose the variation of Ga/N reactant ratio determines the resultant GaN nanostructure morphology due to changing the flow rate of ammonia gas. The type of substrate was found to be a crucial factor in the synthesis of GaN NWs that could be correlated to the lattice mismatch between the bases of grown GaN first nucleus and the type of substrate. High resolution X-ray diffraction confirmed the formation of hexagonal wurtzite structure of resulting materials. Photoluminesces spectra of
GaN nanostructures showed two peaks at a near-band edge emission in the ultraviolet region and a broad emission around the yellow-red region. Three dominant Raman-active phonons corresponding to A1 (TO), E2 (High), and A1 (LO) were observed, which were well-agreed with the Raman selection rules for GaN structure. Apart from that, ammoniating time also showed influence on morphologies of the grown GaN NWs. Morphological analysis indicates growth good quality and high density of NWs with diameters range from 25 to 50 nm and lengths up to tens of micrometers after ammoniating for 30 min. Apart from Ga2O3 and GaN nanomaterials fabrication and characterizations, chemical sensors based on these Ga2O3 and GaN nanostructure have also been developed by depositing pallidum and platinum metals in the form of interdigitated fingers. The gas sensor based on SnO2-coated Ga2O3 NBs showed novel capability in detecting a broad range of H2 concentrations ranged from 33 to 1000 ppm at room temperature as well as other higher operating temperature (i.e. from 80 to 200 oC) for first time. On top of that, this sensor also demonstrated excellent sensing properties such as repeatability and ultra-low power consumption (~2 μwatt). On the other hand, the gas sensor fabricated based on GaN NWs without coating of any metal particles also exhibited very good response toward various H2 concentrations ranging from 7 up to 100 ppm at different operating temperatures. In additional, the coating of Pt nanolayer on one dimensional GaN NWs was also found to be able to further improve the Gas sensing performance of semiconductor nanostructures. The Pt-coated nanowires sensor exhibited the higher response (2650%) when the device was exposed to 1000 ppm H2 gas at room temperature, and it also showed capability in detecting a very low concentration of H2 gas (7 ppm). The sensor based on Pt-coated GaN NWs is found to be the most active for H2 sensing than GaN NWs sensor without coating any
metal catalyst. This study provided a promising method for fabricating gas sensors based on nanomaterials with excellent sensing capabilities at room temperature.
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Keywords
Growth And Characterization Of Ga2o3 And Gan Nanostructures , For Hydrogen Sensing Application