A Study To The Strain Of GaN-based LEDs On Patterned Si Substrate

Recently, a number of major technological breakthroughs have been made in the crystal growth and device fabrication of InGaN/GaN LED. It has been widely used in such as display、backlight and the lighting. Si substrate has a lot of advantages such as low cost, large size, high quality, conducting etc, and the development of silicon substrate GaN based materials and devices will enhence the advantages of GaN based devices with the traditional silicon device technology integration.The Si substrate GaN based LED has made great progress, however it still has some disadvantages in the luminous efficiency, light quality and service life, one of the important reasons is that the difference of lattice constant and thermal expansion coefficient between the Si substrate and GaN film, it will cause the great stress and may result in the cracks of GaN films on Si substrate, the LED luminous intensity, wavelength, light current and voltage are also influenced by the stress.This paper studied the stress and the influence of patterned Si substrate GaN based LEDs, including the influence on the photoelectric performance and the changes of tress in the fabrication processes of LED, and the results as follows:1. We studied the stress distribution in the different area of a single mesh with the Raman test; gain the the thickness of p-GaN layer and the In continent in quantum wells by using SIMS test on the center and corner area of one chip; and the width of quantum wells of these two areas is tested by TEM.2.We cut the GaN film of large size (1200×1200μm2)into small pieces (200×200μm2) by the lithography technology. And found out that the chips in different are show the different wavelength and the light intensity.The chips in the center area has longer wavelength and smaller light intensity than the corner ones. To eliminate the intensity differences caused by the selection of light extraction efficiency, we packaged10center chips and10corner chips to eliminate the phenomenon of total reflection, the test results show that they still have light intensity difference.3.The change of stress is very complex in the chip fabrication processes.and the technics has great influence of the stress distribution. This paper discussed the changes of the stress in the chip manufacturing processes of two samples with different thickness of the buffer layers, and discussed the stress in the center and corner area in the fabrication processes. The stress of the two samples are variation difference in the manufacturing process, but when the chip is completed, the difference is reduced and the stress decreased.4.The stress of GaN film is extremely reduced and well-distributed after been transferred on the wax substrate, which indicated that the right transfer technic may reduce the tress of GaN film and make it well-distributed.It has great meaning of the chip fabrication process.