We have investigated the performance of GaN-based blue light-emitting diodes (LEDs) with a p-InGaN/GaN short-period superlattice (SPS) contact layer, which were grown by metal organic chemical vapor deposition. It was found that dot-like features appeared on the surface when a p-InGaN/GaN SPS structure was grown. The LED operating voltage decreased from 3.52 V to 3.15 V and the electrostatic discharge properties of LEDs were improved by using such a SPS structure. The output powers of LEDs were also increased by adjusting the In mole fraction in the SPS. However, the lifetime of LEDs became shorter when such a SPS structure was used.
In this paper, monochromatic double‐crystal X‐ray diffraction and white‐beam X‐ray topography techniques using synchrotron radiation source were utilized to investigate the growth process of large sapphire crystal by an improved Kyropoulos‐like method. Compared with the calculated theoretical value of 8.6 s, FWHM experimental values of sapphire are in the range of 11 ∼ 26 s, showing its good crystalline perfection in general, especially for the crystal in the central region of the boule. The analysis of white beam transmission X‐ray topographs revealed the presence of dislocation tangles and helical dislocations in different crystal regions. The defect configurations in sapphire crystals were caused by the dislocation reaction and void formation.
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