Abstract
We optimized the deposition conditions of polycrystalline nanoporousGaN coatings produced by Chemical Vapor Deposition on Si substrates, by exploring the effect produced by the Ga holder shape, the initial amount of Ga, the reaction deposition time and the metallic catalyst used. Such polycrystalline films probed to act as antireflective coatings by reducing the reflectance of Si substrates by 50% or more, and that of flat GaN samples by 40% in the UV and 83% in the visible, at the same time that they exhibit an almost constant reflectance from 400 to 800 nm, important to develop UV sensors with enhanced sensitivity. Furthermore, the polycrystalline nanoporous coatings we developed exhibit hydrophobic behaviour, with a static contact angle of 119°, and a contact angle hysteresis of 4.5°, which might contribute to enlarge the durability of such functional films, by the self cleaning effect induced.
Highlights
Nowadays, antireflective coatings are common components used in windows, solar cells, display technology, sensors and eyeglasses to increase quantum efficiency and reduce light pollution[1,2]
Antireflective and hydrophic surfaces in gallium nitride (GaN) have been demonstrated in GaNnano-flowers fabricated by Chemical Vapor Deposition (CVD)[15], and in N-polar GaN surfaces nanostructured by wet photochemical etching under UV illumination and chemically functionalized with lauric acid[16]
We demonstrated the possibility of producing nanoporousGaN by using the direct reaction between metallic Ga and NH3 in a simple Chemical Vapor Deposition (CVD) system[19]
Summary
As can be seen in the image, the contact angle of the water droplet increases substantially from 57° ± 0.7° for the bare Si substrate to 119° ± 3° when the Si substrate is coated with a layer of nanoporous GaN particles This indicates the hydrophobic character of the coatings we developed, they did not reach the superhydrophobic regime. Our surface shows a hydrophobic character due to the air trapped within the surface protrusions[17], consistent with the Cassie-Baxter model we assumed
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