Surface Antireflection and Light Extraction Properties of GaN Microdomes

GaN microdomes were fabricated and measured as both an antireflection surface and a light extraction enhancement structure. The combination of self-assembled micro/nanosphere lithography and reactive ion etching process was used to fabricate GaN microdomes with different aspect ratios. SiO₂ microspheres with diameters of 1000 and 500 nm, deposited on top of the GaN substrate using a dip-coating method, serve as the mask for the formation of GaN microdomes. The GaN microdome shapes and sizes were determined through control of the plasma etching conditions. The antireflection properties of the GaN microdomes with different sizes and shapes were characterized. Two different mechanisms were proposed to explain the surface reflection properties of incidence wavelength below and above GaN band gap, respectively. The trend shows that the surface reflection is reduced with the increase in the aspect ratio of the GaN microdomes for incidence wavelength above the band gap. For incidence wavelength below the band gap, the trend is totally different. Studies indicate that the microdomes are applicable not only as antireflection structures in solar cells but for enhancing light extraction in light-emitting diodes as well.