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Effects of The Sapphire Substrate Thickness on The Performances of GaN-based LEDs

GaN-based light-emitting diodes (LEDs) prepared on sapphire substrates with different thicknesses were fabricated and characterized. By thinning the sapphire substrate to 50 µm, it was found that we can achieve a larger output power under high current injection without increasing the operating voltage. Life tests also indicate that the LEDs prepared on a thin sapphire substrate are more reliable.

During the process of heteroepitaxial growth, if the lattice constant of the growing film differs from that of the substrate, the wafer surface bows, regardless of whether the lattice mismatch occurs or not. As the growth in large-scale wafers speeds up, bowing effects are becoming more and more important. Wafer bowing has a direct impact on the yield in modern mass-production compound semiconductor industries. By using finite element analysis software, the bowing deformation of the GaN wafer on sapphire substrate can be studied. This paper summarizes the causes of bowing deformation, builds the mathematical model, and deduces the relation equation of the wafer bowing. The results show that epitaxial wafer bowing has a linear relationship with the square of the diameter of the substrate but has little relationship with the thickness of the substrate. Moreover, the relation equation of the wafer bowing is also simplified finally.


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