A Study On The Reliability Of GaN LEDs On Si Substrate

GaN based LED has been demonstrated a large potential for applications in Opto-electronic devices. In recent years, GaN based LED Si substrate has made great progress, which are advancing the industrialization. While the reliability of GaN based LED Si substrate needs to be further studied.Current accelerated aging experiments under different stresses on LED chips have been carried out. The light intensity and forward voltage don't change obviously during the process of aging under the stress of 600mA within 30 minutes, though the size of LED chips is only 300μm×300μm. That indicates quality of LEDs made by our laboratory is good. Moreover, current accelerated aging experiments on LEDs have also been done under stress of 20mA, 30mA and 50mA, respectively. The relations of parameters with aging time have been analized in details, which show the light intensity on normal direction decreases obviously, and that can be expressed by high energy of short wave and its negative effect on epoxy resin of LED. But the light output power decrease slightly. The results show that the performance of LED chips is good.In order to improve the performance of LEDs, the influence of submount, the shape of electrode and the chip size on LEDs have been studied. And the properties of two different GaN LED chips have been tested before the chips are scribed. The L-I curves and I-V curve are measured, and current accelerated aging experiments under 1A current stressed on these chips have been performed. The results indicate that the chips with Cu submount can be saturated at higher current, having better luminous output efficiency, moreover, its forward voltage fluctuates less with driving current, and its power declined less during aging experiments. All these mean that the reliability of chips on Cu submount is much better. This suggests that LEDs on Cu submount have great potential for the application on the high power LED devices. We do experiments on two kinds of chips with different electrode shapes as well, and the results manifest that the chips with round electrode are better the ones with electrodes are circle with four forelands. In addition, the experiments on chips with two different sizes have also been performed. The results show that the performance of LED chips with size of 300μm×300μm are superior to the latter 200μm×200μm, which can be attribute to the effect of current crowding.We believe these results would be benefit for further improving the performance of GaN based LEDs on Si substrate.This work is supported by 863-project of China and electronic development program in China.