Characterization study of GaN-based epitaxial layer and light-emitting diode on nature-patterned sapphire substrate

Chemical wet etching on c-plane sapphire wafers by three etching solutions (H ₃PO ₄, H ₂SO ₄, and H ₃PO ₄/H ₂SO ₄ mixing solution) was studied. Among these etching agents, the mixing H ₃PO ₄/H ₂SO ₄ solution has the fastest etching rate (1.5 μm/min). Interestingly, we found that H ₂SO ₄ does not etch the c-plane sapphire wafer in thickness; instead, a facet pyramidal pattern is formed on the c-plane sapphire wafer. GaN light-emitting diode (LED) epitaxial structure was grown on the sapphire wafer with the pyramidal pattern and the standard flat sapphire wafer. X-ray diffraction and photoluminescence measurement show that the pyramidal pattern on the sapphire wafer improved crystalline quality but augmented the compressive stress level in the GaN LED epilayer. The horizontal LED chips fabricated on the pyramidal-patterned sapphire wafer have a larger light output than the horizontal LED chips fabricated on the standard flat sapphire wafer by 20%.