Growth and characterization of InGaN-based light-emitting diodes on patterned sapphire substrates

The microstructure and electrical properties of the InGaN-based blue light-emitting diodes (LEDs) fabricated on patterned sapphire substrates (PSSs) with parallel grooves have been investigated. The PSS with parallel grooves (ridge: 2 μm; trench: 3 μm) along the (11–20) direction were etched using an inductively coupled plasma etcher with different etching depths. From the transmission electron microscopy observation, the PSS was confirmed to be an efficient way to reduce the threading dislocation density in the GaN epilayer. The output power of the PSS LED (461 nm) showed 33% higher than that of the conventional LED. For a typical lamp-form PSS LED operating at an injection current of 20 mA, the output power and external quantum efficiency were measured to be 7.1 mW and 10.1%, respectively. The achieved improvement of the output power is not only due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, but also due to the enhancement of the extraction efficiency using the PSS. Finally, better reliability of the PSS LED performance was also observed.